NOVELTY - Preparing copper rosinate involves mixing copper salt and alkali liquid, agitating the mixture to form uniform suspension, then slowly dipping the suspension into solution of rosin and solvent, raising temperature to 70-90 degrees C, subjecting the product to normal pressure dehydrating reaction, filtering the product to obtain 20-50% solution of copper rosinate, and analyzing and detecting the content of the product.    USE - The method is useful for preparing copper rosinate, which is used in composition (in the form of microemulsion, water emulsion, miscible oil, suspension agent, wettable powder, suspension emulsion or water dispersible preparation) for preventing and controlling plant diseases and insect pests, preferably bacterial leaf blight, banded sclerotial blight, rice blast or cloud disease of rice, green sickness, root rot, tan spot disease, brown spot, stem wilt, rot disease, rust disease, leaf blight or powdery mildew of cotton, soybean, wheat and tobacco, bacterial angular leaf spot, scab, leaf blight, edge blight, yellow top, downy mildew and pustule of cucumber, melon, watermelon, Hami melon, pumpkin and balsam pear, bacterial melasma, soft rot, canker sore, anthracnose, spot anthracnose, powdery mildew, Peronophythora disease and white rot of cabbage, orange and grape, bacterial melasma, bacterial wilt, Phytophthora boehmeriae, yellow or gray mold, tan spot disease, soft rot, streak virus and pustule of eggplant and hot pepper, blotchy ripe disease, green peel disease, bacterial wilt and pustule, ginger disease, yellow top and rot disease of green onion, garlic, ginger, potato and taro, bacterial angular leaf spot and rust disease of kidney bean, towel gourd, green bean and Artemisia selengensis Turcz, bacterial calico, melasma, stem wilt and fruit rot disease of strawberry, celery, radish and Asparagus, sour rot, Rhizoctonia solani infection, anthracnose, leaf blight, mildew and leaf blight of longan, anthracnose, leaf blight, Peronophythora disease, sour rot and root rot of lychee, epidemic disease, leaf disease, greige beige spot disease, anthracnose, sooty mold and sprout wilt of loquat, banana scab, Cladosporium cucumerinum infection, banana rot, anthracnose, yellow-black leaf blight and bacterial wilt of banana, citrus yellow shoot, scab, bleeding disease, canker sore and penicilliosis of pomelo, and Peronophythora infection, anthracnose, and mites infection of mango (all claimed).    ADVANTAGE - The method is simple and environmentally-friendly, and widens the application range of copper rosinate.    DETAILED DESCRIPTION - Method for preparing copper rosinate, involves mixing copper salt and alkali liquid, agitating the mixture to form uniform suspension, then slowly dipping the suspension into solution of rosin and solvent, where in the dipping process, the color of the solution gradually becomes green from blue and the heat release phenomenon is generated, cooling in time and dipping for about 20-40 minutes, after dipping, raising temperature to 70-90 degrees C, subjecting the product to normal pressure dehydrating reaction using a water distributor, after dehydrating, filtering the product using a standard filter paper to obtain 20-50% solution of copper rosinate, and analyzing and detecting the content of the product. An INDEPENDENT CLAIM is included for use of the prepared copper rosinate with a chemical composition for preventing and controlling crop diseases and insect pests.