Abstract: Based on the NCEP FNLs analysis data, this paper studies the mechanisms of convective rain belts developed near the warm edge of western North Pacific subtropical high (WPSH) on 23 July 2012 and 2 July 2013 from the following aspects such as dynamics, vapor, thermal factor and instability. The environment condition analysis shows that WPSH has obvious inner dynamic, thermal factor and instability borders, and the convective rain belts take place nearby the borders.Within the dynamic border of WPSH, there is a downward motion in large range. But on the left side of the dynamic border, there is a weak upward motion. The air is warmer and wetter within the vapor and thermal borders of WPSH, but colder and drier outside. The convective instability within the instability border of WPSH is deeper than that outside. On the left side of the dynamic border and within the vapor, thermal and instability borders, the profitable upward motion, adequate vapor and instability conditions are beneficial to the development convection rain belts near the edge of WPSH. The dynamic, thermal and instability borders of WPSH well correspond to the development of convective rain belts, which shows that the physical meaning of the borders is clearer than the 588 dagpm isoline and is more significant for forecasting the convection development in the warm area near the edge of WPSH.