The pulse establishment process, the influence of pump energy and pulse width on the output laser is analyzed, and a gain-switched Fe:ZnSe laser pumped by an E-O Q-switched Cr, Er:YSGG laser with a wavelength of 2.79 μm and a repetition frequency of 2 Hz at room temperature is also designed. The variation of output laser pulse with pump energy is obtained, and it shows that the number of Fe:ZnSe laser pulses increases from 1 to 7 as the pump energy increases from 10.6 mJ to 25.3 mJ. When multiple pulses are generated, the amplitude of adjacent pulses gradually decreases, while the pulse width and interval gradually increase. Due to multiple pulses, the pulse widths of the Fe:ZnSe laser increase compared with a single pulse, and the peak power of the laser increases slowly with energy. This study has a reference value on the peak power control of the gain-switched Fe:ZnSe laser, and also the laser applications.