Software process improvement (SPI) is a knowledge- and learning-intensive activity that is critical in software development. The literature reveals several major knowledge-based antecedents, namely, exploration, exploitation, absorptive capacity (AC) and knowledge sharing (KS), that are shown to be crucial for SPI. Since SPI is a gradual implementation program, from this perspective, the different roles and effects of these antecedents and how they are associated with various levels of progress in SPI success remain unknown. To address this gap, we propose a research model that combines the four antecedents to examine their comparative influence on successful SPI implementation. To reflect the different levels of SPI success, we employ capability maturity model integration (CMMI) maturities. A survey method is used to examine the model based on 413 CMMI-certified organizations in China. The results show that KS has the most explanatory power in contributing to SPI success at all maturity levels. In a further investigation of different maturities, we find that the dominant knowledge antecedents vary depending on distinct maturity levels. The rationale for the above findings, as well as the theoretical and practical implications and limitations of this study, are discussed and summarized.