A planetary transmission system with bevel gears subjected to axial modification comprises an internal bevel gear set and an external bevel gear set which are in meshing transmission. External bevel gears in the planetary transmission system have non-involute tooth profile subjected to axial modification, and internal bevel gears have standard involute tooth profile. The internal bevel set and the external bevel set realize parallel axis transmission. As the external bevel gears are modified by the form grinding process, 'local conjugate' of a certain amount of transmission errors is caused when in meshing of the gear set, vibration and noise of planetary gears in transmission can be reduced effectively after load is applied, and accordingly the comprehensive performance of domestic high-speed heavy-load planetary gear reducers (increasers) can be improved.