Fourier transform is one of the keys of the mathematical tools in digital signal processing. The performance of traditional discrete Fourier transform based on digital circuit is restricted to the electronic device speed, which is difficult to meet the requirements of the high speed of signal processing, especially restricting the development of Tbit/s super-speed optical processing technology. The discrete Fourier transform method based on the parallel optical vector matrix on time-multiplier principle is studied. The features of high speed and low heat dissipation of light are utilized and putting all optical parallel discrete Fourier transform method with phase only spatial light modulator as the core of transformation matrixes is put forward, which gets verifications by means of experiment. The experimental results show that the proposed all optical parallel discrete Fourier transform has less error (about 0.13). With further modulation and promotion of function, the method can have widely potential application in the high speed optical signal processing.