The invention relates to a measuring method and a measuring system of a driving gear mounting distance adjusting spacer and a driving gear bearing pre-tightening torque adjusting spacer of an integrated main reducer assembly. The measuring system comprises a first detection service position for completing axial data measurement of a combination piece of an internal bearing and an external bearingof the driving gear, and a shell of the main reducer, a second detection service position for completing data measurement of the combination piece of the internal bearing and the external bearing of the driving gear, and a rigid distance sleeve and an electronic control system; an induction signal of a displacement sensor at the first detection service position is converted to obtain a value of the axial data measurement of the combination piece of the internal bearing and the external bearing of the driving gear, and the shell of the main reducing gear; the induction signal of the displacement sensor at the second detection service position is converted to obtain a value of the axial data measurement of the combination piece of the internal bearing and the external bearing of the drivinggear and the rigid distance sleeve; and the desired spacer value is obtained by computing with a mathematical model program. The technical scheme helps eliminate interference of human factors and improve measurement precision.