<p>The integrated performance calculation of the coaxial high-speed helicopter/turboshaft engine is an important part of the coaxial high-speed helicopter/engine matching design, but there is a lack of research in this area. In view of this, a performance calculation method for coaxial high-speed helicopter engine based on power matching is proposed. Firstly, the simplified calculation model of the required power of a coaxial high-speed helicopter is established, and the power calculation result has an error of 4.47% compared with the power curve of the X2 helicopter, which verifies the accuracy of the model. On this basis, the calculation model of engine performance matched with the required power of a coaxial high-speed helicopter is established. Taking the T800 engine of X2 helicopter as an example, the engine performance curve is obtained and its change law is analyzed through numerical simulation; and the change relationship of minimum power speed with altitude and power turbine speed is investigated: for every 1&#xa0;km increase in altitude, the minimum power speed increases by about 3.5&#xa0;m/s, but the minimum power speed is basically unchanged as power turbine speed changes; meanwhile, the sensitivity results of engine performance parameters variation with altitude, speed and power turbine speed under two typical working conditions are obtained: in the case of higher and lower flight speed, the performance parameters do not change in the same direction with altitude, change in the opposite direction with speed, and change in the same direction with power turbine speed. This method can be applied to the pre-study process of actual coaxial high-speed helicopter/engine matching design, filling a certain gap for research in this field.</p>