For a two-mirror reflecting telescope, if the position of primary mirror is set as standard, the influences of de-center, tilt of a aspheric secondary mirror and de-space between primary and secondary mirrors on wavefront aberration of the felescope are analyzed. An error correction method of the telescope is proposed based on the theory. The method firstly uses the radius of spot diagram on axis and secondly uses the mean radius of all fields spot diagrams as performance metric of imaging quality. The position of secondary mirror is adjusted by stochastic parallel gradient descent (SPGD) algorithm. Finally, the mean radius of all fields spot diagrams converge to regard as the situation of best imaging quality. The process is achieved in a Ritch-Chretien (R-C) telescope by computer simulation, and the results show that the correction of secondary mirror makes the mean radius of all fields spot diagrams converge. The method gives the error correcting of the telescope an external standard and can be used to correct error in observation process of the telescope.