Accurately modeling learners’ knowledge states is crucial for advancing personalized intelligent education. However, existing knowledge tracing methods often overlook the influence of problem complexity on students’ answering strategies, leading to unstable and inaccurate predictions. To address these challenges, we propose PSKT, a novel deep knowledge tracing model that integrates problem complexity and state stability. PSKT incorporates (1) a quantitative representation of problem complexity using information entropy and accuracy, (2) dynamic adjustments of knowledge states based on perceived and actual problem difficulty, and (3) a contrastive learning-based mechanism to stabilize predictions and reduce information bias. Experiments on four public datasets–ASSIST2009, ASSIST2015, Algebra05, and Statics2011–demonstrate that PSKT outperforms six state-of-the-art models, achieving up to 3.67% higher AUC and improved robustness across all datasets. These results highlight the potential of PSKT to enhance predictive performance and provide more reliable insights into students’ learning processes, making it a valuable tool for personalized education systems.