This paper theoretically analyzed the design and operating parameters of a pipe-shaped air-cushion surge chamber (PS-ACSC). A mathematical model for a small load disturbance (SLD) in a hydropower plant containing the PS-ACSC was established to analyze the effects of the sensitivity of its initial horizontal area and the air–water volume ratio on the operational stability of the plant. The results showed that the PS-ACSC should occupy a critical horizontal area, and its initial water level and the initial air–water volume ratio should be within a certain range to ensure its own stable operation as well as that of the turbine units. The results of a case study showed that a hydropower plant containing the PS-ACSC is most stable when the initial air–water volume ratio ranges from 2.90:1 to 6.68:1. In addition, a hydropower plant containing the PS-ACSC delivers better performance than a horseshoe-shaped ACSC under the same conditions. This study contributes to the design and operational control of hydropower plants containing the PS-ACSC.