Yb∶Er co-doped Al₂O₃ films fabricated by the technique of the medium frequency magnetron sputtering were sculptured to rectangle waveguide amplifiers(YECDWA) with beeline channel. The relationship between net gain and pump power was measured. The results show that net gain of the YECDWA increases approximately linear as pump power is increased. The threshold is 18mW. The net gain of the 2.24 cm long YBCDWA is 8.44 dB pumped under 68 mW. The numerical simulation displays,however,that net gain of the YECDWA is 10.6dB pumped under same power.