NOVELTY - Screening and transforming a crude oil degrading-marine microorganism comprises selecting the superior strains highest in the degradation rate, adding nitrogen and phosphorus nutrients to it so as to screen out a strain relatively low in dependency on the nitrogen and phosphorus nutrients; and gene engineering modification: constructing the gene xylE of the coding catechol-2,3-dioxygenase to a vector and then transferring the same into the crude oil degrading microorganism screened out such that the catechol-2,3-dioxygenase is efficiently expressed.    USE - The method is used for screening and transforming a crude oil degrading-marine microorganism (claimed).    ADVANTAGE - In the method above, catechol-2,3-dioxygenase is transferred into the indigenous microorganism by a molecular biological method to achieve efficient expression. The crude oil degradation rate can be 62.9% after the strain after is cultured in a crude oil-inorganic salt culture solution containing 5 g/L oil for 15 days. The dependence of the strain on nitrogen and phosphorus nutrients is low with respect to other strains. The strain is a superior strain for petroleum degradation. The strain may well grow in a cheap soybean meal culture medium and has a potential of being thrown into a crude oil polluted sea area for ocean restoring through large-scale solid fermentation.    DETAILED DESCRIPTION - Screening and transforming a crude oil degrading-marine microorganism comprises (a) screening: inoculating sea mud mixed seawater into a crude oil-inorganic salt culture solution for enrichment culturing, where the crude oil-inorganic salt culture solution comprises the following components: 1 g ammonium nitrate (NH4NO3), 1 g dipotassium hydrogen phosphate (K2HPO4), 0.1 g magnesium sulfate (MgSO4), a trace amount of iron phosphate (FePO4), 5 g crude oil which is sterilized by a 0.2 pm microfiltration membrane, and 1000 ml stale seawater; the pH of the crude oil-inorganic salt culture solution is 7.2; after culturing for two weeks by 220 rounds per minute (rpm) at 30 degrees C, diluting the enrichment culture solution to 10-4 to 10-6 times by a 10-time dilution method; adding 2% agar to the crude oil-inorganic salt culture solution to form an oil-containing solid culture medium, applying 0.1 ml diluted culture solution to the oil-containing solid culture medium for culturing at the constant temperature of 30 degrees C, and setting two repeats for each concentration; after culturing at the constant temperature for 48 hours, selecting superior, different-color and different-form single-colony crude oil degrading-marine microorganisms; performing streaking separation and purification on an oil flat plate to obtain a constant-form single colony; measuring the crude oil degrading capacity of the microorganisms by ultraviolet spectrophotometry, selecting the superior strains highest in the degradation rate, adding nitrogen and phosphorus nutrients to it so as to screen out a strain relatively low in dependency on the nitrogen and phosphorus nutrients; and (b) gene engineering modification: constructing the gene xylE of the coding catechol-2,3-dioxygenase to a vector and then transferring the same into the crude oil degrading microorganism screened out such that the catechol-2,3-dioxygenase is efficiently expressed, through the following steps: (i) obtaining the gene xylE of the catechol-2,3-dioxygenase used from a plasmid PIJ4083; (ii) connecting xylE to an efficiency expression vector pWHM3 which contains a strong promoter ermEasteriskp suitable for Streptomyces avermitilis, where the plasmid is Escherichia coli-S. avermitilis shuttle type high copy plasmid; and (iii) transferring the constructed pWHM3-xylE into the microorganism; employing a protoplast transformation manner and adding in 0.4 M cane sugar during the transformation process as an osmotic pressure stabilizer.