With the development of the image content, screen content (SC) images generated by computers begin to spread. In order to code the screen content more efficiently, a new tool named palette mode is added into the High Efficiency Video Coding (HEVC) to improve the compression performance, but it will greatly increase the computational complexity and coding time. We propose an adaptive palette mode decision algorithm based on the complexity analysis of the video content. The proposed algorithm divides the luminance component of the image into blocks and applies discrete cosine transform (DCT) to measure the complexity of each block. Then a judge matrix is derived based on the complexity values. Finally, the coding unit information and the judge matrices are used to judge whether to enable or disable the palette mode. According to the experimental results, compared with the anchor encoder that enables the palette mode, the total encoding time saving of the proposed algorithm can reach 69.24% of the total encoding time saving when the palette mode is disabled, with averagely 0.33% of the bjntegaard delta bit rate (BDBR) increase and 0.03 dB of the bjntegaard delta peak signal-to-noise ratio (BDPSNR) decrease.