In order to study the expression level of let-7a in HaCaT exposed to UVB real-time qPCR was used to detect the expression level of let-7a at 2 h, 4 h, 8 h, 12 h and 24 h after UVB irradiation. Online database PicTar can be used to predict the targets of let-7a and performed function categories with softerware Gostat. The results show that the expression level of let-7a at 12h is higher than that at other time points with more than 7 times. The target prediction and Gostat analysis indicate that casp3、bcl2l2、map3k1 and cdk5 may be UVB-induced target genes of cell cycle regulation. These results suggest that let-7a may play a key role in the mechanism of UVB-induced injury.