In　order　to　assess　the　market　power　issues　for　the　case　of　hydropower　plants　participating　in　the　power　market　competition,　this　article　proposes　multi-stage　stochastic　dynamic　programming　model　of　system　operation.　In　the　dynamic　programming　model,　the　decision　in　each　stage　and　each　state　is　the　equilibrium　of　multi-agent　game　and　the　equilibrium　point　is　solved　by　iterative　algorithm.　Case　studies　show　that,　from　the　view　of　long-term　operation,　the　price　of　hydropower　plants　decentralized　dispatch　is　much　higher　and　fluctuate　more　severally　than　the　situation　of　system　optimal　dispatch.　Meanwhile,　taking　bilateral　contracts　as　market　power　mitigating　measures　and　setting　rational　contract　electricity　and　contract　price　can　decrease　the　price　level　and　control　its　fluctuation　effectively.