Based on the self-developed standard process RF-LDMOS device, a new ultra-wideband RF power amplifier is designed in this letter. The amplifier removes the absorbing resistor and capacitor series structure at the end of the drain. The stability of the circuit is enhanced by the pre-matching circuit. Considering the small impedance value of the RF high-power device, it is difficult to achieve broadband matching. The novel tapering drain transmission has been developed which overcomes the distributed amplifier’s limitations of low power and efficiency. Ultra-wideband RF amplifier has excellent output power and efficiency. The measurement results show that from 0.8-2.2GHz, under the condition of 28V power supply, the saturated output power is 43dBm (20W), the power gain is 10dB, the drain efficiency is about 30%-50%; The peak-to-average ratio is 8dB, and the ACPR is less than -41dBc when the linear output is 5W, proving the effectiveness of the new tapered drain structure to achieve broadband.