In laser bending forming, the warping deformation influences forming accuracy of laminated plate. Therefore, the research of warping deformation in laser reciprocating scanning process has practical significance. Based on ANSYS software, a finite element model (FEM) was built. By simulating temperature field, stress field distribution and the free end deformation of the laminated plate, the mechanisms of warping deformation in single-pass reciprocating scanning process were analyzed. The results show that with the increase of reciprocating scanning number, a large variation of temperature makes heat energy equally distribute at both ends of scanning line, and thermal stress increases due to the cumulative effect of heat in the middle area. After each laser scanning, the residual stress on the bottom surface has an accelerating effect on warping deformation of the next scanning in laser action zone, which makes chordal height increase from 0.217 mm to 0.363 mm after scanning one to six times. However, as scanning number increases, the reduction in the promotion effect slightly decreases the growth of chordal height, and its maximum value is 0.058 mm. The max error of temperature field between the experiment and simulation is 9.85%, the max error of Z-direction displacement on warping line is 4.33% and the error of chordal height is 2.16%, which lays a solid foundation of calculation for better bending quality of the laminated plate.