Long-term durable remission in patients with B cell malignancies following chimeric antigen receptor (CAR)-T cell immunotherapy remains unsatisfactory, often due to antigen escape. Malignant B cell transformation and oncogenic growth relies on efficient ATP synthesis, although the underlying mechanisms remain unclear. Here, we report that YTHDF2 facilitates energy supply and antigen escape in B cell malignancies, and its overexpression alone is sufficient to cause B cell transformation and tumorigenesis. Mechanistically, YTHDF2 functions as a dual reader where it stabilizes mRNAs as a 5-methylcytosine (mC) reader via recruiting PABPC1, thereby enhancing their expression and ATP synthesis. Concomitantly, YTHDF2 also promotes immune evasion by destabilizing other mRNAs as an N-methyladenosine (mA) reader. Small-molecule-mediated targeting of YTHDF2 suppresses aggressive B cell malignancies and sensitizes them to CAR-T cell therapy.