The invention discloses a method of coaxially aligning two fiber gyroscopes. The method comprises the ten steps of constructing a fiber gyroscope measurement system, establishing a coordinate system of the fiber gyroscope measurement system, defining each included angle of a fiber gyroscope sensitive axis in a space, measuring initial positions of fiber gyroscopes, calibrating the position of the fiber gyroscope sensitive axis OZ', deducing and adjusting a relational expression between the plane and fiber gyroscope mounting planes, establishing a three dimensional model, calculating the thickness of a gasket, selecting the specification of a filler gauge, machining the gasket, and aligning the fiber gyroscopes, so as to finish the coaxial aligning of the two fiber gyroscopes, wherein the fiber gyroscope measurement system comprises a main fiber gyroscope (1), a standby fiber gyroscope (2) and a mounting structure body (3). By coaxially aligning the two fiber gyroscopes, the problem of large measuring error caused during the use of the standby fiber gyroscope is solved; by aligning the two fiber gyroscopes by virtue of the coaxial aligning method, the absolute values of calibrated angles alpha and beta are less than 1'.