The invention discloses a synthesizing method of a polyolefin nucleating agent aldol compound. Sorbic alcohol and xylitol respectively react with p-tolualdehyde, p-ethyl benzaldehyde and 3, 4-syringic aldehyde; p-toluene-sulfonic acid serves as a catalyst, cyclohexane serves as a solvent and methanol serves as an accelerant to synthesize 6 nucleation agents, i.e., DMDBS, EDBS, MDBS, DMDBX, EDBX and MDBX, and the like. The optimized conditions are obtained by experiments, i.e., the feed mole ratio is 2.1: 1.0; the dosages of the p-toluene-sulfonic acid, the cyclohexane and the methanol are respectively 4.0 percent, 580 percent and 430 percent of a reaction base substance; reaction time is 6 hours. The method has the advantages of easily obtainable raw materials, simple technique, short reaction time, and the like. The prepared nucleating agent represents obvious influences on the crystallinity of PP and PE; when the adding quantity of the nucleating agent is 0.3 percent to 0.5 percent, the crystallinity is maximal.