In this paper, we propose a layered screen video coding scheme based on existing video codecs to leverage hardware video codec for efficient screen video compression. In this scheme, the screen video compression is performed as two-layer coding: base layer coding and enhancement layer coding. The screen video is first analyzed in both frame and block levels for useful temporal and spatial information extraction to assist coding content selection in each layer. The non-skip screen frames are directly compressed by the conventional video codec in the base layer, while the screen contents sensitive to the video quality degradation are selected for improved coding in the enhancement layer. For contents to be enhanced, two intra coding modes are designed to improve the quality of the compressed text/graphics contents and suppress the artifacts introduced by chroma downsampling. The experimental results demonstrate that the screen video quality is improved objectively and subjectively by the proposed scheme with low cost on bitrate and computation complexity. Moreover, an average of 2.95dB coding gain is achieved in high bitrate.