OFDM　technology　has　become　the　core　technology　of　DTMB　system.　The　high　Doherty　power　amplifier　can　effectively　improve　the　peak-average　power　ratio　of　OFDM　system,　but　with　poor　linear　performance.　This　paper　starts　with　improving　linear　performance　of　Doherty　power　amplifier,　analyzes　the　nonlinear　model　of　power　amplifier,　presents　a　construction　method　of　nonlinear　performance　model　of　Doherty　power　amplifier,　gets　the　corresponding　nonlinear　performance　curve,　and　then　presents　a　design　of　pre-distorter　which　can　improve　system　linear　performance.　The　nonlinear　performance　curve　is　used　to　do　the　simulation.　The　result　shows　that　the　system　linear　performance　is　improved　greatly.