A preparation method of multielement organic compound fertilizer is characterized by that the waste steel slag with alloy structure in metallurgical industry, industrial waste acid, and animal and plant organic metters are made into mother fertilizer, and ternary fertilizer of nitrogen, phosphorus and potassium is added so as to obtain the invented multielement organic compound fertilizer which contains complete nutrients necessary for growth of crops, and features durable fertilizer effect, good adversity resistance and high utilization rate. The test results show that it can increase crops yield by above 15-35%, can loosen soil and raise water-retaining and fertilizer-retaining capacity of soil, and can reduce production of insect pest and plant diseases.