A reflective optical pulse shaping system based on liquid crystal spatial light modulator was built. With changing the modulation voltage loading into the pixel on the liquid crystal spatial light modulator, the system resolution and the relationship between the output including intensity and phase and the modulation voltage were measured. And the modulator′s calibration was discussed. The resules show that the intensity changes with modulation voltage linearly, while the phase is nonlinear. The frequency resolution of pulse shaping system is 10 GHz, corresponding 0.08 nm wavelength resolution, which can realize the modulation of optical signal with frequency interval of 10 GHz. An optical frequency comb with 10 GHz spectral spacing was adoped as the light source. Spectrum shaping was performed and flat spectrum, Gaussian spectrum, triangular spectrum and inverted triangle spectrum were generated experimentally.