Amidst the challenges posed by the Covid-19 pandemic, this study investigates the impact of Problem-based Language Learning (PBLL) using DingTalk on enhancing Business English Writing skills among Chinese undergraduates. Employing a mixed-method approach, the research involved two phases. In the quantitative phase, a twelve-week quasi-experimental study was conducted. The control group received traditional Business English Writing instruction, while the experimental group utilized the PBLL + DingTalk method. Analysis of pre-test and post-test scores using SPSS 27.0 revealed a significant improvement in the experimental group's writing abilities, with their post-test scores averaging 5.3275 points higher than the control group. In the qualitative phase, semi-structured interviews were conducted with students from the experimental group. Participants expressed high engagement, motivation, and satisfaction with the PBLL + DingTalk approach, highlighting its effectiveness in interactive problem-solving and technology integration. This study demonstrates the effectiveness of PBLL + DingTalk in improving Business English Writing skills among Chinese undergraduates, even during challenging circumstances like the Covid-19 pandemic. The combination of quantitative results and qualitative insights underscores its practical impact and relevance for language educators, emphasizing the importance of innovative teaching methods in adapting to evolving educational landscapes.