In this paper， a wide band cascode power amplifier working at 33~170 GHz is designed， based on the 500 nm InP dual-heterojunction bipolar transistor （DHBT） process. Two pairs of parallel input and output stub lines can effectively expand the working bandwidth. The output coupling line compensates the high frequency transmission. The measured results show that the maximum gain of the amplifier is 11.98 dB at 115 GHz， the relative bandwidth is 134.98 %， the gain flatness is ±2 dB， the gain is better than 10 dB and the output power is better than 1 dBm in the operating bandwidth.