The electromagnetic fields in a thrust magnetic bearing considering electromagneto temperature coupling during the rotor startingup are investigated for a kind of magnetic bearing rotor systems in which the heat source comes mainly from the eddy current loss due to solid thrust disk.The analytical calculated method (ACM) of eddy current loss is presented.It indicates that in preliminary design the system parameters can be expediently determined by comparing the numerical results of ACM with the results of finite element method (FEM) and experiments.