The invention relates to a method for determining inertial navigation element performances based on a flight test and theoretical calculation. The method comprises the following steps of acquiring actual measurement frequency of an unmanned plane inertial navigation element, acquiring theoretical measurement frequency of the unmanned plane inertial navigation element, and comparing the actual measurement frequency and theoretical measurement frequency of the unmanned plane inertial navigation element, wherein if the absolute value of the difference of the two frequency values is less than or equal to a certain threshold value, the inertial navigation element can satisfy unmanned plane flight frequency measurement requirements or not, otherwise. The method solves the problem that at present, an unmanned plane with flight test attitude can only measure a time domain value and cannot measure frequency domain data, and provides a trusted measurement means for inertial navigation element performance assessment.