Abstract: By reasonably designing the pendulum length, the natural frequency of a pendulum structure can be effectively reduced, so that it can realize resonance under low frequency (even ultra-low frequency) vibration excitation, and then greatly improve the energy conversion performance. The pendulum-type triboelectric nanogenerator (P-TENG) has naturally become the focus of academic attention. In this study, nonlinear electromechanical coupling modeling and parameter sensitivity analysis are conducted to optimize the structural design of the P-TENG, so as to promote its development towards engineering practicability. Based on the analysis of power generation mechanism, an equivalent capacitance model is proposed. Combined with the energy principle and equivalent circuit method, an electromechanical coupling model considering the nonlinear variation of pendulum angle is established. Using the harmonic balance method and alternated frequency/time domain technique, the steady-state output of the P-TENG is solved analytically, and the stability of the results is determined. Numerical integration and dynamic tests are conducted to verify the accuracy of analytical model. The results are compared with the linear model and the influence of various design parameters on the output characteristics of the P-TENG is investigated. Considering the nonlinear effects, the estimated operating bandwidth of the model increases significantly (by a relative increment of 83%). The proposed model can effectively avoid the underestimation of the operation bandwidth and significantly improve the accuracy of the P-TENG performance estimation. Increasing the excitation amplitude, reducing the damping ratio, and minimizing the electrode angle can improve the output performance of the P-TENG. Various fitting models have been proposed to model the relationship between design parameters and output performance. The fitting coefficients obtained from the parameter influence discussion can be used as the basis for the P-TENG output performance design.