This letter presents a simple approach to design ultra-broadband power amplifiers (PAs). The theories of the hybrid modes class-EFJ PAs are applied. The relationship between the operating frequency and load impedance is analyzed for class-EFJ PAs. By appropriately selecting load impedances at different frequencies, a PA can work well in 1.0-4.0 GHz with high efficiency. In addition, the second harmonic impedance is obtained by combining the selected fundamental impedance and load-pull simulation. For validation, an ultra-broadband high efficiency PA is implemented. Experiments show that output power is from 40.1 dBm to 42.6 dBm and drain efficiency is between 60.6% and 72.7% at the saturation level in 1.0-4.0 GHz. The ACLR is smaller than -27.2 dBc in the same frequency band with an average output power of 35.2 dBm.