A blood pressure measurement device and a calculation method thereof are disclosed. The blood pressure measurement device includes a pressurizing motor unit and an exhaust valve unit in communication with an airbag unit. The blood pressure calculation method includes steps of controlling the pressurizing motor unit to pressurize the airbag unit; measuring pressurized measurement data from the airbag unit in a pressurization process; controlling the pressurizing motor unit to stop pressurizing the airbag unit, and controlling the exhaust valve unit to depressurize the airbag unit; measuring depressurized measurement data from the airbag unit in a depressurization process; extracting blood pressure parameters from the pressurized measurement data and the depressurized measurement data; calculating an average of the blood pressure parameters extracted from the pressurized measurement data and the depressurized measurement data, to obtain a blood pressure measurement result.