In order to investigate the mechanism of formation of self-generated magnetic field in laser plasma interaction, the self-generated magnetic field was theoretically analyzed and numerically simulated. Using kinetic theory here the self generated magnetic field is generated by the nonparallelism of the temperature gradient and density gradient when the intense laser injected to the thin plasma target. The time evolution relation of the spatial distribution of the self generated magnetic field is obtained. The results show that when laser injected the plasma target, self generated magnetic field is generated on the surface of the plasma. Because of the nonparallel density gradient and the temperature gradient, this magnetic field considerably affects the absorption of laser and various transmission processes of laser.