Abstract: The quality of frequency spectrum of transmitted signal could affect the quality of moving target indicator detection of radar. The factors, such as modulation pulse, harmonic component of electric network and working state of the klystron, are analyzed, which have the influence on transmitter frequency spectrum quality. A series of experiments are processed on a experimentalmodel with klystron. Then, a mass of experiment data is offered to prove the effects on the transmitter frequency spectrum quality.It is of benefit to the engineering application of the transmitter with klystron.