An ejector cooling system with thermal pumping effect (ECSTPE) could operate without consumption of electric power, but it discards a great amount of thermal energy, which generally results in a lower COP value and a greater chilling load. An innovative concept for the optimal initial ratio is therefore proposed to develop the optimal time length of cooling stage (TLCS) control method. The optimal TLCS control method effectively improves the ECSTPE performance. First, in this context, it was theoretically proven that the optimal initial ratio could be used to reduce the energy loss and the chilling load. Second, it was formulated how to achieve the optimal initial ratio; and the optimal TLCS control method was determined by identifying the relationship between the TLCS and the initial ratio. Third, case studies were conducted to demonstrate the effectiveness of the developed optimal TLCS control method on ECSTPEs with different refrigerants. The results showed that for ECSTPE with R134a, a 10-second deviation from the optimal TLCS led to a decrease of 5.6% in the COP value and an increase of 23.7% in the chilling load. For ECSTPEs with R141b and R365mfc, a 10-second deviation led to relatively slight performance deterioration; however, an excessive deviation (e.g., 100 s) would lead to severe performance deterioration (e.g., increases of 35% and 58% in the chilling loads for ECSTPEs with R134b and R365mfc, respectively). The developed optimal TLCS control method could certainly improve the performance of ECSTPEs with other refrigerants. (C) 2016 Elsevier Ltd. All rights reserved.