Discussion on the thermal equilibrium process of the heating effect on the first crystal of a double crystal monochromator (DCM) for synchrotron radiation is presented. A testing method as well as the results of thermal effect on photon flux of U7C DCM are introduced

which is under the thermal load from a 6T single-period superconducting wiggler at NSRL. The finite element method is used to calculate the temperature distribution and thermal strain of the crystal. Both steady and transient cases with radiation cooling alone and with a combination of radiation and forced convection cooling are considered.