The quantum random number plays an increasingly important role in information security because of its unpredictability and true randomness. Most of the existing random number generation protocols assume that the light source obeys a certain distribution probability and then estimates the minimum entropy of random number extraction from the measured value. However, due to the imperfections of the actual light source devices, the distribution of light intensity fluctuates to some extent. If the intensity fluctuation is ignored in the process of calculating the minimum entropy, the calculated minimum entropy value will be too large and the safety will be affected. If the traditional method is used to consider the fluctuation of light intensity, the estimation result will be too poor and the size of the randomness that can be obtained will be reduced. In order to solve this problem, this paper proposes a quantum random number generator with a light source monitoring function, and takes the self-testing quantum random number generator protocol based on dimension witness value as an example. Simulation results show that by adding a light source monitoring module at the source part, the upper and lower bounds of the single-photon contribution can be more tightly estimated, and higher minimum entropy and randomness can be obtained compared with the traditional method. This scheme provides a useful tool for the practical application of the quantum random number generator.