The invention discloses a rendering optimization method and a device, wherein the display fluency of images is ensured and the frame-dropping phenomenon is avoided when the drawing and merging function is realized for a variety of types of mobile terminals. According to the method, the caching operation is conducted for a plurality of established rendering commands and vertex data associated with each rendering command. After that, the judgment and the analysis on the data volume of the vertex data, the GPU of a display card and a currently adopted operating system are conducted. If the data volume of the currently cached vertex data is smaller than or equal to a vertex data threshold, and / or the GPU belongs to a logic type set and the currently adopted operating system belongs to a system type set, at least two rendering commands among the plurality of rendering commands and having the same material identifier are merged. All merged rendering commands are then drawn. Finally, the vertex data associated with each rendering command are copied into a consecutive system memory and then are sent to a graphic rendering application program interface from the system memory.