Objective To study the stability of micro-implant orthodontic anchorage (MIA) with different pitch in the case of immediate loading. Method Employing 3d finite element analysis method, the stress and displacement distribution on the bone interface of MIA with different pitch (0.3mm、0.5mm、0.7mm and 1.0mm, respectively) , which was 1.47N loaded vertically in the major axis direction, were analyzed. Result The pitch affected the stress distribution significantly, because the maximum stress increased with pitch increasing and the impact of pitch on stress distribution on the neck and the central location of MIA were different; to decrease the pitch could reduce the max displacement of the jaw,but the impact of pitch on displacement distribution of MIA was not significant. Conclusion In the case of immediate loading,MIA with pitch 0.5mm-0.7mm should be selected as orthodontic anchorage in the clinic.