How to control and manipulate the heat flow in a flexible way is a hotspot of current research. Based on Laplace's equation, we propose a method to design thermal cloak of arbitrary shape. For a thermal cloak of regular shape, the thermal conductivity expression is derived by analytically solving the Laplace's equation under certain boundary conditions; for a thermal cloak of irregular shape, the distribution of thermal conductivity can also be obtained based on the numerical solution of Laplace's equation. Results of full wave simulation show that no heat fluxes emerge in the internal stealth area both for two-dimensional and three-dimensional thermal cloak of arbitrary shape. Meanwhile, the heat fluxes return to their original pathways, resulting in a perfect thermal invisible effect. This research provides a feasible method to design a thermal cloak of non-conformal cross section and has a guiding significance for the design and manufacturing of thermal cloak.