Abstract: A general thermal vacuum test takes a time span of 7 to 30 days for a whole test process. As the number of tasks increases, the test pieces sometimes have to queue up for being tested. This paper studies the problem of the test piece queuing for the thermal test in the medium-sized space environmental simulation chamber. The test tasks in a group of space environment simulation chambers during the past five years are analyzed. It is shown that the arrival interval of the test pieces follows a negative exponential distribution approximately, while the test duration is in the Gamma distribution approximately. Based on the analysis of the data, a M/G/k queuing model is established. The average length of the queues, the average queuing time and other key indicators under the conditions of different number of tasks and different test durations, are calculated by the Monte Carlo method. The study provides a reference for the construction and the optimization of similar test facilities in the future.