NOVELTY - Preparing organic soluble chitosan derivative (I) by solid liquid heterogeneous reaction, comprises: adding chitosan into an organic amine and chloroalkane mixed solution and placing the mixed solution; dissolving a long-chain acyl chloride in trichloromethane and gradually dripping the solution into the mixed solution of the chitosan and performing a reaction; heating the solution and refluxing the solution; filtering the reaction mixture and collecting the filter liquid organic phase; and performing the rotary evaporation to the filter liquid and vacuum-drying the filter liquid.    USE - (I) has antitumor- and antimicrobial-activity. (I) is useful: to strengthen human body immunity; in food, cosmetic, textile, printing and dyeing and paper making industry, preferably in the biomedicine field; as wound dressing, postoperative adhesion material and drug carrier. No biological data given.    ADVANTAGE - The process: is simple, easy, cost effective and eco-friendly for preparing (I) with no toxicity, good biocompatibility and biological degradability.    DETAILED DESCRIPTION - Preparing organic soluble chitosan derivative of formula (I) by solid liquid heterogeneous reaction, comprises: adding chitosan with a deacetylation degree of 70-90% and weight-average molecular weight of 3000-800000 into an organic amine and chloroalkane mixed solution with the volume ratio of 1-4:1 and placing the mixed solution for 48 hours; dissolving a long-chain acyl chloride of which the mole number is 0.5-4 times mole number of the reactive hydrogen on the chitosan in trichloromethane to obtain the solution (30-60 mass%) and gradually dripping the solution into the mixed solution of the chitosan and performing a reaction at room temperature for 3-5 hours; heating the solution to 80 degrees C and refluxing the solution for 6-12 hours; filtering the reaction mixture to separate the solid from the liquid, and collecting the filter liquid organic phase; and performing the rotary evaporation to the filter liquid and vacuum-drying the filter liquid to obtain the organic soluble chitosan derivative that can be dissolved into various organic solvents.    m+n = 1;    n = 0.7-0.9;    x = greater than 0 to less than n;    y = greater than 0 to less than m;    R = CO(CH2)n1(CH)3; and    n1 = 4-16.