The airworthiness certification is necessary before the aircraft enters into the commercial operation. The requirement of the airworthiness is the basic regulation guarantee for the safe flight of aircraft; therefore it is necessary to study the airworthiness certification method for gas turbine engine emissions. In order to solve the technical difficulty of the methods involving gas turbine engine emission test data and meet the requirement for engine emissions airworthiness certification standard, an emission measuring system is designed with reference to Aircraft Engine Emissions promulgated by the convention of ICAO. The accuracy of this system is no more than 7%, it is much better than 10%—15% based on the procedure for the analysis and evaluation of gaseous emissions from aircraft engines requirement, so that the sampling and measurement system is proved feasible. Calculation of NO_x emission index from aircraft is developed by using ICAO method based on the ICAO standard involving Landing and Take-Off (LTO) cycle. JT3D-7 NO_x emission is compatible with the existing regulatory standards according to CCAR-34. According to the method of ICAO, a system for the airworthiness certification of gas turbine engine emissions is developed by MFC and NO_x emission index of the engine could be quickly computed.