Two-dimensional macroscopic temperature field of the work-piece and evolution of the microstructure which is located at the bottom of the melt pool in coaxial laser cladding are calculated. Formation of the clad bead due to powder feeding is simulated. Macroscopic temperature field is computed. Then, one macroscopic cell at the bottom of the melt pool is re-meshed for calculation of the microstructure evolution. Initial temperature conditions are calculated with interpolation method among the temperatures of its nearest neighbor macroscopic cells. Its four boundary temperatures can be considered as the same as its four neighbors′ temperatures. Crystal nucleus is set in the lower boundary of microscopic domain. Finally, phase field and temperature field are calculated using phase-field method. The calculation results agree with the experimental results, which proves the validity of the macro and micro coupling model.