Based on the development of thermal metamaterials, numerous novel heat devices were reported to realize the continuously increasing demands in the field of thermal management. In this paper, we proposed an efficient optimization method for the design of illusion thermal device which can provide an artificial signal of heat source for devices to conceal the real ones. The key for the reported optimization method is a model of heat flux manipulation formulated according to the topology optimization. With the formulated model, we realize the design of illusion thermal devices in a typical condition. Besides, a kind of double-layer device are proposed to realize more flexible location camouflage of heat source. Compared with the traditional methods, the new design method is suited for more flexible shapes and distances of artificial heat sources, and has a better adaptability in the broad field of heat flux manipulation.