For an Er3+/Yb3+ co-doped microring resonator, formulas of the transfer function and output power gain are presented, transmission characteristics are analyzed, and simulation is performed. Around the pumping wavelength of 0.98 μm and the central signal wavelength of 1.55 μm, the effects of the pump power, signal power, dopant concentration and amplitude coupling ratio on the output power gain are investigated, the transmission spectra are presented and the optimization of the device is carried out. Simulated results show that the output power gain of this device is much larger than those of the Er3+/Yb3+ co-doped straight waveguide amplifier with the same waveguide length. In the case of the pump power of 8 mW, signal power of 36.5 μW, Er3+ ion concentration of 1×1026 m-3, and Yb3+ ion concentration of 3×1027 m-3, the signal power gain of the device can reaches 11.6 dB and even 60 dB. Also, this device is propitious to the denser integration in the opto-electronic circuits.