An air intake valve apparatus for pneumatic tool, configured in an intake port of a pneumatic tool for controlling air circulations, mainly comprises a valve base configured in the intake port of the pneumatic tool, a stem configured through the valve base inside capable of shifting to a air-blocking position and a air-exhausting corresponding to the valve base and a flexible component propped the stem for keeping the stem on the air-blocking position regularly, wherein the stem has a first portion, a second portion and a mid-reducing portion, the mid-reducing portion is coupled to the first portion and the second portion respectively with different transiting surfaces so as to maintain the force driving the stem in constant no matter the air pressure entering the valve base is lower or higher.