Abstract: There is thick gypsum in the Fourth Member of Shahejie Formation in Dongying sag.The gypsum has the thermal property of high thermal conductivity and low thermogenesis, which can affect the thermal evolution of source rock. Taking the source rock,near the deep gypsum,as the study subject,the thermal effect of gypsum to source rock is analyzed using the indexes of Ro,Tmax and crystallinity of illite. The thermal evolution between the areas of gypsum and non - gypsum is contrasted.Because of the thermal property of gypsum,the geoheat under the gypsum conducts upwards and the geothermal gradient decreases,which makes the tendency of thermal evolution of source rock slow.The geoheat under the gypsum accumulates near the top surface of gypsum,which makes the degree of thermal evolution of source rock near it increased quickly,and the thermal evolution indexes has a leap near it.The source rock in non-gypsum area has the normal thermal evolution.This study has theoretical significance to the generation of oil&gas and a guide role to the exploration practice of deep oil&gas of this area.