To improve the low rate of temperature monitoring of medical steam sterilizers, caused by testing technology, a temperature monitoring system based on a fiber Bragg grating (FBG) was designed, and its feasibility, accuracy, and reliability of temperature measurement for the whole sterilization process were studied. First, to meet the related standards for temperature monitoring of medical steam sterilizers, an FBG array sensor was designed using wavelength-division multiplexing technology. Then, the corresponding temperature monitoring system was constructed, and the whole sterilization process was monitored in real time. Finally, the accuracy of the detection system was verified by analyzing the temperature changes with time at each stage of the sterilization process, the sterilization time under the effective sterilization temperature range, and the maximum temperature difference between points under no-load, half-load, and full-load. The monitoring results accurately showed the temperature changing with time during each stage of the sterilization process. The effective sterilization time is 7.8 min for the monitored sterilizer, and the maximum temperature difference of each point in the cavity is within 2 ℃ for no-load and 4.5 ℃ for full-load. The temperature measure range and resolution, time recording accuracy, and data storage capacity of the system met national and industry standards. Moreover, the proposed system possess superior characteristics over traditional systems, displaying the potential for economical multi-point monitoring and the ability to enter the narrow area for monitoring.