The modulation transfer function (MTF) has been widely used to characterize and quantify the spatial resolution of a linear and space-invariant imaging system. Various methods have been proposed to determine the MTF of an imaging system. A new analytical line spread function (LSF) fitting model to calculate the MTF is proposed. The LSF parameters are confirmed by means of a nonlinear least-square fitting technique. Compared with previous models, the MTF estimate based on proposed model shows the lowest error in the presence of different noise. A practical application of MTF measurement in degraded image restoration also validates the accuracy of proposed method.