The power amplifier plays a privotal role in the military electronic systems in the present. The combiner, an important component of the RF power amplifier, needs to face the challenge of high combining efficiency, high power tolerance, wideband and miniaturization. This paper takes the width matching cascading scheme to design a 4-way power combiner in 8~12 GHz based on offset parallel-coupled cascade structure. The test result shows that the output isolation is <-15 dB, the standing wave loss is <-19 dB, and the combining efficiency is >78.7%. And the power amplifier system is developed with the size of 52 mm×38 mm×5.5 mm, based on the 4-way power combiner. The experimental results show the maximum output power is 52.2 dBm and the insert loss is <1.4 dB. Compared with the conventional microstrip coupler, this kind of power combiner is more compact, more efficient in synthesis, better in isolation, and more capable of withstanding power, which can apply to satellite communication, radar station and electronic countermeasure.