TECHNOLOGY FOCUS - BIOLOGY - Preferred Process: The optimized culture condition is: a culture medium at 15-26 (preferably 20) degrees C; the specific growth rate of the algal cells at maximum temperature of 20 degrees C; the initial pH of 6.5-8.5 (preferably 7.5); the specific growth rate of the algal cells at the optimum pH of 7.5; and the illumination intensity of 54-108 (preferably 54) mu mole/m2/second-1, where the algal cells are exuberant in growth and the biomass live weight of the cells is maximum when the illumination intensity is 54 mu mole/m2/second-1. The heterotrophic culture medium is formed by adding 0.1 mass% of glucose to the autotrophic culture medium. The autotrophic procedure comprises: culturing cells to a logarithmic phase under the following conditions, where the inoculation density of the Nitzschia closterium is 2.5x 105/ml, the volume ratio of the Nitzschia closterium to the autotrophic culture medium is 1:10, the initial pH is controlled at 7.5, the culture temperature is 20 degrees C, the illumination intensity is 54 mu mole/m2/second-1 and the ventilatory capacity is 5 l/l; and then naturally precipitating the autotrophic liquid, centrifuging and separating the liquid, retaining the autotrophic algal cell precipitate. The heterotrophic large-scale culture procedure comprises: re-suspending the autotrophic algal cells in the heterotrophic culture medium, where the initial density of the cells is 10x 105/ml; when starting the heterotrophic culture, regulating the oxygen saturation to be 100%, controlling the temperature at 18-22 degrees C, keeping the ventilation rate at 150-250 l/hour, controlling pH of the heterotrophic system of 6.5-8, controlling the stirring speed at 120 revolutions per minute, controlling the illumination intensity at 54 mu mole/m2/second-1, when the cell density is greater than 100 g/l, ending the fermentation; controlling the total heterotrophic time in 200-300 hours; collecting the algal cells from the heterotrophic liquid by a solid liquid separation technology, freezing and drying the cells; and storing the cells in the form of solid dry powder. The oil in the algal cells is extracted by a solvent leaching method.    TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preparation (Claimed): Preparation of (I) comprises: optimizing a culture condition; preferably selecting an autotrophic culture medium and a heterotrophic culture medium; and performing amplification culture with the autotrophic culture medium and performing large-scale culture with the heterotrophic culture medium.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The autotrophic culture medium is composed of sodium nitrate (74.8-120 (preferably 105) mg), sodium dihydrogen phosphate (4.5 mg), sodium metasilicate nonahydrate (50-150 (preferably 100) mg), ferric citrate pentahydrate (3 mg), vitamin B1 (220 mu g), vitamin B12 (0.22 mu g) and sodium chloride (3.6 g), which are dissolved in artificial seawater (1000 ml), where the artificial seawater is composed of magnesium chloride (4.98 g), potassium bromide (0.096 g), sodium fluoride (0.003 g), strontium chloride (0.024 g), boric acid (0.026 g), sodium bicarbonate (0.192 g), calcium chloride (1.102 g), potassium chloride (0.664 g), sodium sulfate (3.917 g) and sodium chloride (23.476 g), which are soluble in distilled water (1 l) and the initial pH is regulated to 7.5 with 0.1 mole/l of hydrochloric acid and/or sodium hydroxide.