The invention provides slow-release fluid suspension composite fertilizer. The slow-release fluid suspension composite fertilizer comprises 30-200 parts of fertilizer nutrients, 0.05-2 parts of a thickening agent, 0.1-4 parts of a suspending agent, 0.1-3 parts of an emulsifier, 0.05-1 part of a nitration inhibitor and 0-15 parts of water. The fertilizer nutrients comprise nitrogenous fertilizer, phosphate fertilizer, potash fertilizer, humic acid and trace elements and also contain at least one quick-acting fertilizer and at least one slow-release fertilizer. The invention also provides a preparation method and a use method of the slow-release fluid suspension composite fertilizer. The slow-release fluid suspension composite fertilizer has the advantages of the existing fluid suspension and is ternary liquid fertilizer containing the quick-acting and slow-acting nutrients, trace elements and humic acid, prolongs fertilizer efficiency of the suspension fertilizer, realizes combination of trace elements, humic acid and fertilizer, continuously and stably provides nutrients needed by crop growth and development, and solves the problems of nutritional deficiency symptom and later fertilizer removal in crop growth.