The error of line transfer frequency from Time Delay Integration(TDI)CCD has strong influence on dynamic Modulation Transform Function(MTF) and it is stronger when the integral grade is higher.Therefore,this paper develops an accurate mathematical model for dynamic MTF and line transfer period error rate was developed. Firstly, a typical line transfer timing of TDICCD was introduced and the window functions of one integral grade and multiple integral grade were derived. On these bases, the relationship between line transfer period error rate and dynamic MTF for this timing was established by Fourier transform of the window functions and a nonlinear parameter was derived in the function which is none in the traditional one. Then, simulations and experiments were performed, which indicate that when ΔT/T=0, the dynamic MTF value for this timing is 0.632 5 times of static MTF with the number of phases b=4. It also indicates that there are obvious differences between dynamic MTF curves from proposed method and traditional method. Finally according to the requirement of the index, the maximum line transfer period error rates with different integral grades are given, which ensures that the decline of the dynamic MTF is less than 5%.