The invention discloses a coupling and decoupling measurement method of a machine tool geometric error. The method comprises the following steps: decomposing a machine tool geometric error into a moving shaft and a rotating shaft and then carrying out decomposition to obtain a displacement error and an angle error; expanding the circumferential surface of the rotating shaft into a moving shaft guide rail plane at an equal ratio; measuring an axial displacement error of each shaft directly and measuring the planeness of the guide rail plane of each shaft by using a dial indicator; acquiring a plurality of unilateral coupling errors for each shaft; carrying out linear fitting on the coupling errors, carrying out decoupling to obtain a displacement error term and an angle error term, averaging repeated measurement terms to obtain six geometric errors of each shaft; and on the basis of the measured 36 geometric error terms, calculating a geometric error of the machine tool by using a homogeneous transformation matrix. According to the invention, angle errors and displacement errors of all shafts of the machine tool can be measured at the same time with the high error measurement precision and the quantitative analysis of influences of all geometric errors on the precision of the machine tool is realized, so that improvement of the control and machining precision of the geometric errors of the machine tool are facilitated.