The security of traditional cryptographic algorithms is based on the black-box attack model. In this attack model, the attacker can only obtain the input and output of the cryptographic algorithm, but not the internal details of the cryptographic algorithm. In recent years, the concept of white-box attack model has been proposed. In the white-box attack model, attackers can not only obtain the input and output of cryptographic algorithm, but also directly observe or change the internal data of cryptographic algorithm. In order to ensure the security of existing cryptographic algorithms under white-box attack environment, redesigning the existing cryptographic algorithms through white-box cryptography technology without changing their functions is called white-box implementation of existing cryptographic algorithms. It is of great significance to study the design and analysis of the white-box implementation scheme for solving the issue of digital rights management. In recent years, a kind of side channel analysis method for white-box implementation schemes has emerged. This kind of analysis method only needs to know a few internal details of white-box implementation schemes, then it can extract the key. Therefore, it is the analysis method with practical threat to the existing white-box implementation schemes. It is of great practical significance to analyze the existing white-box implementation schemes to ensure the security of the schemes. The typical representative of this kind of analysis method is the differential computation analysis (DCA) based on the principle of differential power analysis. This study analyzes the Bai-Wu white-box SM4 scheme based on DCA. Based on the research results of the statistical characteristics of n-order uniform random invertible matrix on GF(2), an improved DCA (IDCA) is proposed, which can significantly improve the analysis efficiency on the premise of almost constant success rate. The results also show that the Bai-Wu white-box SM4 scheme can not guarantee the security in the face of DCA, therefore, it must be further improved to meet the security requirements of practical scenarios.