The invention discloses organic-inorganic composite flower fertilizer for prolonging florescence and a preparation method thereof. The organic-inorganic composite flower fertilizer for prolonging florescence is prepared from seaweed meal, undaria powder, hypnea powder, potassium borate, decomposed goat manure, agricultural organic fertilizer, humic acid potassium salt, zinc sulfate, ammonium bicarbonate, soybean meal, corn bone powder, silkworm excrement, biological zymophyte, bentonite, diatomite, auxin, decomposed chicken manure, urea, fulvic acid, humus, trace elements, plant ash, a soil raising agent, manganese sulfate, magnesium sulfate, borax, a water-retaining agent and clay. The organic-inorganic composite flower fertilizer has advantages of organic fertilizer and inorganic fertilizer, improves flower stress resistance and disease resistance, improves a flower fertilizer absorption capability, reduces a soil hardening degree, improves a soil ecological environment, improves flower quality, has a simple formula, is convenient for use and accelerates a flower growth rate and prolongs florescence after application.