Abstract: The pulse formation process in a passively mode-locked multi-core photonic crystal fiber laser with saturable absorber was investigated experimentally and numerically. The starting procedure included relaxation oscillation, Q pulses and finally stable mode-locking. The oscillation tendency between the cores was almost the same because of the strong evanescent coupling between the cores. The research shows that ensuring the coupling efficiency, the fine adjustment of fiber input coupling is not required for stable mode locking.