Abstract: The bulk and weight of radar on UAV are restricted so severely. Meanwhile, the efficiencies of radar's main power devices are also an important parameters. We must consider adequately these factors to design transmitter as making great efforts toimprove purity spectrum and reliability. This paper introduces three focuses about the design of minitype SAR transmitter on UAV.There are parameters calculation and TWT calorifics emulation and test results given out after demonstrating on principle about every important units. And these results indicate that the transmitter, with high purity spectrum and excellent reliability, meet fullywith minitype SAR on bandwidth, power and smoothness.