Aiming at the high complexity of the mathematical model of short channel transistor, a gm/Id method is proposed to describe the short channel transistor model. This method optimizes the circuit performance by establishing the relationship between the circuit index and transistor size. The experiment result shows that the transimpedance amplifier with a photodetector capacitance of 250 fF can achieve a gain of 59.72 dBΩ, a bandwidth of 3.445 GHz, an input referred current noise of 6.209×10-3 nA/sqrt/Hz and equivalent input noise current of 876.0 nA. The design dissipates 7.5 mW from a 1.2 V supply. The test results show that, when 100 μA current is input, the peak to peak data jitter of the circuit is about 64.92 ps, and the output swing is 81.1 mW.