Abstract: Without the power scanning function, the traditional Particle-in-Cell simulation software needs to perform many times in order to achieve multipactor threshold prediction. Therefore, an adaptive scanning method is proposed without considering the self-consistent field generated by electrons. Under the effect of the electromagnetic field distribution calculated by MSAT, the electron motion is tracked and updated with leapfrog algorithm. Secondary electrons are released once electrons reach the boundaries of the simulation region. The criterion for determining multipactor occurrence is established according to the particle number curve via the multipactor simulation. Meanwhile, the power input is adaptively adjusted by the bisection method so that the multipactor threshold can be automatically determined with a given initial power. For verification, multipactor thresholds of stepped impedance transformer and coaxial cavity filters obtained with adaptive-scanning method are compared with experiments. And the simulation results accord well with the experimental data.