The invention discloses an onboard 360-degree around-viewing display method and system. The method comprises the following steps of: S1, enabling a projection module to subject images acquired by respective cameras to viewpoint transformation by looking up a lookup table and to project the images onto a vehicle top view; S2, subjecting the four camera images to optical alignment by using an exposure gain algorithm; S3, splicing the splicing seams of the images acquired by the adjacent cameras by using a splicing algorithm to obtain the vehicle top spliced view. The method reuses the splicing seam of a last frame when the splicing seam at a certain position is not large in adjacent timing sequential difference so as to reduce an influence of noise on the calculation of the splicing seam greatly for improving stability. In addition, the direct use of the splicing seam of the last frame also shortens the calculation time of splicing seam and improves algorithm efficiency.