Based on C. A. Swanberg and P. Morgan's. empirical formula between temperature of silica equilibrium state in groundwater and practical earth heat flow data, this paper calculates the silica heat flow values in the northern segment of North-South Seismic Belt, and gives the outline of silica heat flow isogram of this region. The result shows that the silica heat flow as whole is middle normal value, and the high silica heat flow region is feeble anomaly. In addition, the relation between silica heat flow and tectonics is also discussed.