The present invention discloses a city expressway access ramp vehicle pass guiding system in car networking environment and a guiding method thereof. The system comprises a roadside device, a monitoring center, the vehicle device of a main line vehicle and the vehicle device of a ramp vehicle; the roadside device includes main line traffic stream information collection module, a ramp traffic stream information collection module and a roadside intelligent decision module; the vehicle device of the main line vehicle and the vehicle device of the ramp vehicle respectively include vehicle master control modules, vehicle basic information storage module, GPS location modules, vehicle speed collection modules, vehicle speed control modules and prompting modules; the conflict prediction estimation is performed through the operation station information of the near-side lane vehicle of the roadside device collection main line and the ramp vehicle to give out the grouping condition of the access ramp vehicle and the safety vehicle speed required by importing the main line traffic flow and send the grouping condition and the safety vehicle speed to the prompting module and the vehicle speed control module in the vehicle device. The city expressway access ramp vehicle pass guiding system in car networking environment and the guiding method thereof can avoid the vehicle collision of an express way confluence zone and improve the driving safety and the pass efficiency.