The bionic C library and the graphic system of the Android system were analyzed in this paper. It was found that the memory filling operations of the system took lots of time, so did the alpha compositing operations. The Unicore architecture could achieve better performance when accessing to 32 bytes aligned memory. The assembly language optimization approach was used to optimize the memory filling operation. The characteristics of concurrent operation of the SIMD (Single Instruction Multiple Data) co-processor were utilized to optimize the alpha compositing operation, which could finish the composition in processing several pixels simultaneously. The canvas filling operation was improved by 17% on average and up to 44% in the experiments for 0xbench after implemented with the mentioned assembly optimization approach. The bitmap drawing operation in 0xbench was accelerated by 34% on average assisted by  the mentioned  SIMD accelerated scheme and assembly optimization methods.