Currently most methods cast code summarization generation as a machine translation task. Wherein the Transformer framework is a representative among them. Thanks to the attention mechanism in the Transformer, such a framework has achieved the state-of-the-art performance. Unfortunately, the Transformer encounters a series of challenges when generalizing to code summarization generation domain. Compared with natural language, code sequence is characterized by more complex multi-modal features, and difficult to extract these features only by the original Transformer structure. To further improve the performance, we make full use of code semantic and structural information in abstract syntax tree to build a simple yet effective framework, which consists of self-attention and graph based module to integrate code semantic information and syntax tree structure information. Besides, to compensate for the insufficiency of Transformer in encoding local features, we present a well-designed local RNN module. Extensive experiments show that the proposed method performs on par with the state-of-the-art methods on two public benchmarks, including Java and Python datasets. The comprehensive ablation studies further demonstrate the effectiveness of architecture design choices. The source code is released at https://github.com/tzv314159/SSTrans.git.