Based on the theories of the energy-transfer upconversion (ETU) effects in actively Q-switched solid-state lasers, coupling passively Q-switched rate equations including ETU parameters are established. The ETU effects in the Nd:YAG laser crystals and the Cr4+:YAG saturable absorbers are numerically simulated by a variation stepping Runge-Kuttaa method. The pulse energy and peak power are affected obviously at low pump power, and average power is affected obviously at high pump power. The effects of ETU on the pulse energy and peak power are decreased with the pump power increasing. And the effect to the pulse duration (full width at half maximum) and the repetition rate can be neglected with the pump power increasing. The numerical calculation results are coincident with the experiments.