Due to the gain fluctuation and nonlinear characteristic variation of the TWT amplifier chain, predistorter cannot compensate the nonlinearities at different frequencies within the working band, thus nonlinear mismatch might occur and nonlinearity of TWTA could get worse at some frequencies. The wideband linear match theory of predistorter with TWTA is put forward, and the influence of nonlinear mismatch is discussed. Predistorter cascaded with gain compensation unit can flatten the gain fluctuation and match the nonlinearity of TWTA, truly broaden the linear working band of LTWTA.