The invention relates to a method and device for global illumination rendering under multiple light sources, which are used for the global illumination rendering of a scene comprising a plurality of objects. The method is executed by a system with an internal memory coupled to an external memory and comprises the following steps: respectively processing geometric surfaces and virtual point light sources in the scene to obtain a first number of geometric blocks and a second number of light source blocks; building a light transmitting matrix with all sampling points in the scene as row coordinates and all the virtual point light sources in the scene as column coordinates; dividing the light transmitting matrix into a second number of columns and a third number of rows; calling sub-matrixes and the geometric blocks into the internal memory from the external memory, and calculating the brightness contribution values of the virtual point light sources in the corresponding sub-matrixes to the sampling points; accumulating the brightness contribution values to the corresponding sampling points and outputting the total brightness of the sampling points. The method and the device provided by the embodiment of the invention can effectively increase the global illumination rendering speed and improve the global illumination rendering efficiency and are suitable for rendering of a large-scale external memory scene.