Abstract: Cooling effect of shielding gas should not be neglected during laser cladding process. The fluid model was simplified by transforming thermal and convection problems into hydromechanics and conduction problems, respectively. Cooling type of shielding gas was investigated and the heat dissipation was quantitatively characterized. It was found that convection coefficient was several hundreds times of conduction coefficient.The evaluation results were adopted for calculation of stress and strain of copper powder and AlN matrix exposed to single-pass laser cladding. According to the first and third strength theory, three kinds of cracks were obviously found, including tear cracks in the interface, pull cracks on the upper surface of the base metal and transverse cracks in the cladding layer perpendicular to laser scanning direction. The forming mechanism of cracks was analyzed and the guidance for optimizing process parameters was proposed.