Abstract: Because the rail transit planning in central business district is unable to meet the travel requirements, the construction of Beijing rail transit Line 28 is proposed. This rail transit with "post-construction and supplementary development" characters will face up to poor line condition, special passenger flow and high engineering investment risks, therefore the selection of system standard should be considered comprehensively. Through analyzing the functional localization, line conditions and passenger flow requirements, AGR (automatic guided rail) system and Lb-type vehicle are preliminary selected from 5 medium traffic systems, including straddle monorail system, AGR, low-speed magnetic suspension system, high and low panel articulated vehicle and Lb-type vehicle. After a detailed comparative study of the two selected systems, due to the better line adaptability and system inclusiveness, the Lb-type vehicle is accounted to be more suitable for Line 28 and therefore is recommended.