This paper introduces a design of dual-band Doherty power amplifier for TDD systems. The circuit is different from single-band Doherty power amplifier. Dual characteristic impedance transformers and a novel combiner for Doherty power amplifiers are used to realize the dual-band PA in 1880-1920MHz and 2010-2025MHz. The simulation results of the PA show that the PAE achieves 52% at an average output power of 44 dBm, a 6 dB back-off output power from the peak output power of 50dBm in 1900MHz and 2017MHz simultaneously. The simulation results also clearly illustrate that this dual-band architecture is still valid for a signal with high peak to average power ratio (PAPR).