The invention provides a method for acquiring a crossing key V/C ratio. The V/C ratio of each lane set, the possible route of the phase, the V/C ratio of the route, the V/C ratio of key route of the phase and loss time summation of key routes are comprehensively considered. The key V/C ratio of the crossing is calculated based on the factors, thereby obtaining a more reasonable and more accurate crossing key V/C ratio, thereby facilitating improvement of scientificalness, rationality and timeliness in traffic decision. The invention further relates to a computer system for calculating the crossing key V/C ratio.