Abstract: The effect of double nozzle jet of a rocket to a helicopter is studied by calculating and testing the pressure, temperature and velocity of the flow. A three dimensional Navier Stokes equation is solved with a standard k ε turbulent model. Two experiments were carried out and the total pressure of jet flow was tested. Based on the tests, the differences between the calculated and test results were found to be 3% and 7% respectively. It proved that the results of calculation can well be used in engineering applications