Cu(OH)2 precursor was synthesized by direct precipitation method and CuSO4 and NaOH were used as raw materials. Then, Cu(OH)2 precursor was calcined in muffle furnace at 400°C for 2h in order that CuO particle was obtained. Through the analysis of the factors affecting the CuO, the paper determined the optimum conditions for the synthesis of nano-CuO with the direct-precipitation method. Then the paper analyzed phase composition and crystal structure of samples using XRD and calculated the average grain size of samples by Scherrer formula, and observed and analyzed by TEM to characterize the morphology and particle size of samples. The optimum precipitation conditions are as follows: when the precipitation agent is 3.2:1, reaction time 40min and precipitant concentration 0.6mol.L-1. The average size of CuO particle prepared under the conditions is 18nm and the yield is 96%.