The "Double Reduction" policy (DRP), enacted by the Chinese government in 2021, was primarily designed to reduce students' academic burdens by limiting homework assignments and off-campus tutoring activities. Nevertheless, the policy essentially reshaped the professional responsibilities and roles of teachers, emphasizing a notable increase in non-instructional tasks such as after-school services and psychological counseling. Employing a mixed-method research design, this study explored the relationship among teachers' perceived changes in workload following the DRP implementation, their experiences of role ambiguity and overload, and resultant burnout. Quantitative analysis based on responses from 325 teachers indicated significant increases in non-instructional workloads, which were (in)directly associated with elevated levels of burnout, mediated primarily through increased role ambiguity and overload. Complementing these findings, qualitative insights from semi-structured interviews with 13 teachers provided a deeper understanding. Interviewees highlighted a pervasive role ambiguity arising from unclear standards and expectations surrounding their expanded non-instructional responsibilities, compounded by inadequate institutional training and support. Teachers frequently expressed feeling overwhelmed by diverse new duties, resulting in role overload. They described the necessity of becoming multi-functional professionals to fulfill expectations in areas previously beyond their scope. Furthermore, teachers reported substantial role conflict as these non-instructional duties encroached upon their core instructional responsibilities, causing increased stress, reduced efficiency, and diminished teaching effectiveness. Collectively, these pressures contributed to a pronounced shift in professional identity—from traditional educators toward service-oriented public providers—required to balance multifaceted demands from students, parents, and broader societal expectations. Despite the challenges faced by teachers, the DRP positively impacted students by alleviating academic stress and increasing their engagement in extracurricular physical activities. Yet, the policy's effectiveness displayed notable variability, influenced significantly by regional disparities, economic contexts, and specific professional roles held by teachers (e.g., class supervisors versus non-supervisors, subject-specific teachers with administrative duties), resulting in sharply polarized outcomes.