Abstract: A priority control strategy is proposed on the back pressure regulation of the back pressure extraction steam turbine (BEST) in double-turbine echelon cycle regenerative system power plant. Measures are adopted including control valve on the exhaust piping, replenish steam piping and control valve from auxiliary steam system to the mixing header, overflow valve from the head to next level LP heater, overflow valve from the head to the condenser. The optimized BEST back pressure is chosen to be 0.2MPa during start and 0.6 MPa during normal operation with the limit from 0.09MPa to 0.72MPa. A priority control strategy is proposed with the different control level recommended. The BEST back pressure, pressure ratio between final blades and final blades earlier stage, differential pressure between LP7 & LP8 are all should be under supervisory control under this strategy, so as to ensure the safety operation of the BEST & LPs, with the inlet valve full open. Efficiency under variable unit load is improved under this priority strategy.