X-ray magnetic circular dichroism(XMCD) in absorption has been extensively used to determine spin and orbital moments by applying the sum rules to the absorption spectra of specified atoms. Due to quench of orbital moments in 3d transition metals, it is necessary to reduce errors in experiments and data analysis. In this article we focas on the data analysis in 4 aspects. 1) The influence of applied magnetic field H on signal intensity. Experiments reveal that, for H-α; for H>200Gs, it changes little with the increase of H. 2) There is a separation between absorption spectra resulting from the iron-core remanence being in the parallel or antiparallel directions. This separation is independent of incident X-ray polarization and can be eliminated by multiplying by a constant. 3) An analytic form of absorption spectrum was obtained by fitting experimental data using XPSPEAK 4.1. It can be used as a criterion to determine which numerical integration method is suitable under certain experimental conditions. And, 4) by choosing an error function as a background to be subtracted from the X-ray absorption spectra, a method of calculation of spin and orbital moments from XMCD absorption spectrum is also developed Finally, the spin moment, of 1.314μB and orbital moment of 0.141μB of cobalt atom in a 20nm thick cobalt film are figured out based on Bode rule numerical integration.