For the problem of telemetry communication can not meet the demand of the real-time observing on the ground, this paper proposes a method which applied the envelope analysis to data compression and transmission of flight tests, it provides an effective way for the real-time transmission of telemetry data. First, by picking up the extreme points, interpolating and fitting, the envelope of the telemetry data is acquired. And then the spectrum of the envelope is calculated and according to the sampling theorem, the re-sampling frequency is decided, which could achieve the reduction of data transmission on the premise of maintaining the basic characteristic and change rule of the data. In the end, through processing and analyzing a group of actual telemetry vibrational data, the efficiency of the method was testified.