Capture efficiency (CE) is a critical performance parameter for microchannel plates (MCPs), yet its accurate measurement remains challenging. In this study, we propose an innovative method for evaluating the CE of newly fabricated MCPs based on the detection of a photoelectron beam generated by UV light irradiation of a zinc plate. When incident photoelectrons are detected by the MCPs, they produce a series of disordered pulse signals. We demonstrate that the average pulse interval (denoted as Ts) correlates with the number of electrons entering the microchannels, enabling the assessment of CE differences among various MCPs under identical experimental conditions. Additionally, by partially blocking the incident surface to modulate the active area of the MCP, we established a relationship between Ts and active area, providing a means to roughly quantify CE. This method offers a straightforward alternative for assessing MCP performance, with reduced platform requirements and operational complexity.