As the size of the city expands, longer journeys often involve the use of two or more modes of transportation. Feeder buses perform as a feeder mode of rail transit, its feeder areas are the key factor to improve this bus-rail transit mode service quality. Feeder areas that are either too small or too large can hinder the effectiveness of feeder buses. This paper presents a method to determine a suitable range as the key service of feeder buses for rail transit stations. The modal of accessibility consistency threshold interface of bus and bus-rail transit mode features is established, and the competition area of adjacent stations is considered to calculate the reasonable bus feeder range of rail transit stations. Based on the analysis of the demand characteristics of the feeder passengers, the potential passengers of the bus-rail transit travel mode are defined as the travel where only one endpoint of the starting and ending is within the walking range of the rail transit station, and a method for identifying the points of interest of potential passengers of the bus-rail transit mode is proposed. The potential passenger flow within the reasonable feeder range of rail transit stations is visualized, and the key service areas of feeder buses are determined based on the maximum potential passengers. Taking Jinan Metro Line NO.2 Stations as an example, combined with the station type, the key service area of feeder buses for railway stations is explained.