The invention provides a system design method based on rail traffic bulb circuit. The method comprises the following steps: taking an inflection point of a bulb circuit in a CBTC system as a next or last link object in a section linkage relation on the two sides of the inflection point; ensuring that the CBTC system searches the next or last link object of a current section in which a train is positioned according to the linkage relation and the train moving direction. The method can further effectively compute train envelope crossing the inflection point and judge the consistency of train moving direction and directions of a traffic signal machine and a bumping block, and reduces the proximity computation error of the traffic signal machine and MA computation error. The method ensures that the CBTC system supports bulb circuits, and improves the operation capacity of the CBTC system.