An effective finite-difference time-domain (FDTD) method,timebiased FDTD method,is developed to filtrate high-frequency noise for particle-in-cell (PIC) simulation.The formula is derived using time bias and relaxation iterations on the basis of centered-difference FDTD method.Stability and convergence of this method are analysed. In the computation of a relativistic magnetron,compared with the centered-difference FDTD method,filter efficiency of this method is shown.