To accomplish identification of parameters and force under unknown external force, the velocity, displacement, structural parameters and external force are simultaneously augmented into to the state vector for model formulation, and particle filter with good performance in nonlinear system is then used to identify both the parameters and force. There will be drift of the identified force during force identification due to the lack of velocity and displacement measurement. This paper uses trapezoidal integration and zero-phase high-pass filtering to calculate the velocity and displacement with acceleration. The calculated values are used to adjust the velocity and displacement obtained by particle filter at a specific interval to eliminate the drift. It is demonstrated in simulation that this method can provide relatively accurate estimation results and ameliorate the drift phenomenon during force identification.