Abstract: In the actual engineering layout of pumped storage power stations，there is a certain length of connecting tunnel segment between the lateral inlet/outlet and the gate shaft.At present，there is no selection basis for the cross-sectional type of the connecting tunnel segment in the design process.Therefore，in this paper，the influence of cross-section types （ circular，gate and square ） of connecting tunnel segment on hydraulic characteristics such as head loss，velocity distribution and flow distribution of lateral inlet/outlet was studied by means of numerical simulation.The results showed that under the outflow condition，when the cross-section was square，the internal horizontal diffusion and vertical diffusion were the most sufficient，the hydraulic indexes were better，the head loss coefficient decreased but did not change much，the flow velocity distribution and orifice flow distribution were more uniform，the non-uniformity coefficients of the middle and side orifice flow were less than 1.5，and the non-uniformity degrees of the flow were less than 10%.Under the inflow condition，different cross-section types of the connecting tunnel segment had little influence on the hydraulic characteristics of the lateral inlet/outlet，and all of the hydraulic indexes can meet the specification requirements.The research results can be a basis for the shape design of the connecting tunnel segments.