The main defect of laser seal welding of hemispherical resonator gyroscope(HRG) is the solidification crack at keyhole. In order to solve the problem of air tightness, on the basis of the theoretical analysis of the welding process and the relevant experimental verification by using the “keyhole effect” of laser welding, the mechanism of “misalignment” structure of welding joint to prevent hot cracks is investigated, and a new welding structure is proposed accordingly.The results show that the crack in the welding joint of new structure is restrained and the air tightness is improved significantly.