AD8561 (Analog Device Inc.) MACRO-SPICE model is used to investigate the coupled effects of multiple photocurrents generated by gamma pulse radiation in its Input and Output modules. Firstly, the test circuit is built to find sensitive devices according to previous studies. Besides, Gummel-Poon bipolar junction transistor (BJT) model including photocurrent generators implemented by the exponential current sources is adopted to replace the initial device model. Finally, the effects caused by each photocurrent and multiple photocurrents under different input states are simulated and analyzed. The simulation results indicate that there are competitive relationships among the multiple photocurrents generated in the input-stage bipolar transistors, even in a single bipolar transistor, and the relationship changes with the input state. The transient upset induced by photocurrents generated in the Input and Output modules have superimposed effects on the output ports, but the transient upset duration depends mainly on the Input module.