It is known that there are many structural parameters in the nonlinear multistable energy harvesting system model. Due to the inevitable errors in the process of measurement, processing and assembly, these structural parameters are uncertain. Even slight variation of key parameters may lead to a significant influence on the output voltages. Especially when multiple uncertain parameters exist at the same time, it may have a more complex impact on the energy harvesting performance of the system. Therefore, it is of great value to study the stochastic behavior of nonlinear energy harvesting systems with multiple uncertain parameters. In this paper, a bistable energy harvesting system with double uncertain parameters is investigated. Firstly, the equilibrium point stability and static bifurcation of deterministic bistable systems are analyzed by using RouthHurwitz theorem. Then, by using the orthogonal polynomial approximation method, the stochastic bistable system(TSBS) with two independent uncertain electromechanical coupling coefficients is reduced into an equivalent deterministic extendedorder system, so that the stochastic response problem of TSBS is transformed to the response problem of an equivalent system. After that, from both global and local perspectives, the effects of uncertain parameters on system dynamics and power generation performance are revealed by comparing the attractor, attraction domain, phase orbit, mean square voltage, and energy conversion rate between the equivalent system and the deterministic system. The results show that in some sensitive parameter ranges, the uncertainty of the two electromechanical coupling coefficients will lead to the change of the dynamical motion state of the system, and the greater the intensity of the uncertain parameters are, the earlier the system will enter the chaotic state through the period doubling bifurcation cascade. In addition, under the uncertainty of the two electromechanical coupling coefficients, the mean square voltage will decrease to a certain extent. Compared with the electromechanical coupling coefficient in the electrical equation, the electromechanical coupling coefficient in the mechanical equation has a greater impact on the system. Furthermore, when the two uncertain parameters both exist, the energy harvesting performance of the system changes more significantly.