Abstract: We have obtained altogether heat flux data of 23 drill holes including 2 observational holes of thermal flow in the Haicheng seismic area. These data show roughly thermal structure of crust in east Liaoning and the Haicheng seismic area. The results indicate that there is higher rate of heat flow in the north by east belt from Liaoyang to,Xiongyue, and the average thermal flux is 8.2910-2 J/m2s (2.0 HFU). Average thermal flux in the Haicheng seismic area is 9.2210-2J/m2s (2.2 HFU).Comparing with other known geophysical data of the Haicheng seismic area, we give a geophysical section of synthetic interpretation. We suppose the low-velocity layer in the lower crust of the Haicheng seismic area is a result of large-scale intrusion of upper mantle substance. High temperature and low seismic velocity mean that the layer has the nature of plastic mechanics. The focal region of the Haicheng earthquake is situated right in the upper part of that plastic layer. Obviously, this result is significant for studying the seismogenic process of the Haicheng earthquake and other intra-plate earthquakes.We venture to emphasize that the observation of heat flow is indispensible for earthquake study.