Abstract: In the prototype of the electromagnetic calorimeter (ECAL) of the circular electron positron collider (CEPC), a silicon photomultiplier (SiPM) is used to convert light to electronic signal as part of detector cell. Due to the strong temperature dependence and fast response speed of SiPM, a monitoring circuit is required to monitor its gain and dynamic range by generating pulse light which matches the response speed of SiPM to excite SiPM. In this paper, based on the simulation result, a dual NMOS-based driving circuit and corresponding control circuit were designed. The circuit drives a light emitting diode (LED) to emit nanosecond-level narrow pulse light with adjustable intensity. The photomultiplier (PMT) was used to measure the time-domain characteristics of single LED light emission, and the time width of light pulse is about 10 ns. In the joint test with the electronics of CEPC ECAL, the SiPM monitoring circuit works as expected, and the gain of SiPMs in the ECAL prototype is successfully measured in batches, which meets the self-test requirement of the prototype.