In this paper, the magnetic properties and crystal structure of the PtCo alloys around the equiatomic composition have been studied. The PtxCo1-x (x=0.48,0.49,0.50,0.51) bulk samples are prepared by arc melting and heat treatment. The magnetic measurement results indicate that the increase of platinum content causes the decrease of remanence and the increase of coercivity. The XRD result indicates that the axial ratio c/a of the tetragonal structure decreases with increasing the content of platinum, which leads to an increase of the deviation from unity of the tetragonal structure. So that, the anisotropy field of the ordered phase is improved and the coercivity is increased.