In order to restrain cement kiln shell’s thermal loss and potential safety hazards, composite design was employed of working layer, thermal preservation layer and thermal insulation layer. Thermal preservation layer’s boundary and strain were analyzed and the overall thermal conductivity was calculated. The result shows that the sinusoidal curve boundary combination is adopted between the working layer and thermal preservation layer, and the slopeª²shape with angle of 135 degrees between the thermal preservation layer and thermal insulation layer could relieve the strain concentration. Comprehensive thermal conductivity of the composite mullite brick decreases from the working layer 2.74 W·m-1·K-1 to 1.54 W·m-1·K-1. When applying the composite bricks in cement kilns, the kiln shell temperature is from 50 ¡æ to 70 ¡æ lower than using normal bricks.