We generate a flat temporal-phase distribution optical pulse by 1.3-mm-long photonic crystal waveguide. The effect of coupled pulse energy on the temporal-phase distribution of the output pulse is analyzed by numeral simulating. Simulation results indicate that the root mean square of the output pulse phase decreases to 0.0095 with the optimum coupled pulse energy, which is about 30 pJ, and the narrowest output pulse width is 418 fs. The generation of a flat temporal-phase distribution optical pulse on-chip scale results in potential application prospect in optical communication, pulse compression, pulse shaping and other nonlinear optical application fields.