In this paper, experimental and theoretical studies of the piezoelectric effect of two-dimensional ZnO nanostructures, including straight nanosheets (SNSs) and curved nanosheets (CNSs) are conducted. The results show that the CNSs have a great advantage in piezoelectric property over the SNSs; the maximum output current of the NG based on CNSs was measured to be about 260 nA, much higher than that generated by SNSs. For comparatively analyzing the working mechanics of both NGs, the piezopotential distribution of both CNS and SNS structures was studied using the finite element method. The simulation result that the piezopotential generated by CNSs is always much larger than that generated by SNSs in the case of lateral bending, has more advantages for piezoelectric NGs than the SNSs. This work may provide guidance for structural optimization of piezoelectric nanogenerators and designing high-performance self-powered strain sensors.