As more and more power is consumed in servers, growing attention has been paid to power management. However, little work has been dated on the power-efficiency of query execution plans generated by the DBMS. Traditional optimal query execution plan does not take power-efficiency into account. This paper tries to generate a power-efficient query execution plan by redesigning the query optimizer of the database. We build a power model to estimate the power consumption of a query execution plan and propose an algorithm to generate the power-efficient query execution plan. Using two experiments based on the TPC-H benchmark, we evaluate the accuracy of our power model and compare the power-efficient query execution plan with the traditional optimal query execution plan. Keywords-query execution plan; power-efficiency; power