Point Spread Function (PSF) is an important parameter indicating performance of camera and the important basis for image restoration. In order to solve the problem of uncertainty of initial phase and lack of sample points with single knife-edge, a new method named multi-phase-knife is proposed including design and data processing. Simulation result of two PSF measurement methods based on Monte-Carlo method show that relative measurement error of this method is steady and fewer than 2% by contrast, and relative measurement error of single knife-edge is only about 10%. This method is used in PSF measurement of GF-2 pan-chromatic camera, and the result is validated by double-point, which provides references of engineering application for TDI-CCD PSF measurement.