This is a multicenter, open-label Phase I clinical trial of BEBT-507 in subjects with polycythemia vera(PV). Phase Ia is a single-agent dose-escalation study designed to evaluate the safety, tolerability, pharmacokinetics (PK), preliminary efficacy, and pharmacodynamics of BEBT-507 in subjects with PV . Based on the results of Phase Ia, two doses will be selected for further evaluation in Phase Ib to assess the efficacy, safety, and PK profile of BEBT-507 in subjects with PV , and to recommend a dose for Phase III clinical trials.