The FEA result of the first crystal of double crystal monochromator (DCM) at SSRF

which is exposed to Wiggler source and cooled by liquid nitrogen was reported. The slope error of the surface exposed to high thermal load is 2.33μrad. We also try to calculate the full width at half maximum (FWHM)of the crystal rocking curve by SHADOW software. The result indicates that design of cooling system and method are quite enough to meet with the requirement of DCM. And it is an efficient way of predicting optical parameter of DCM by calculating the FWHM of rocking curve of crystal with thermal distortion by SHADOW.