The invention relates to a method and a system for measuring datum points of a vehicle body, and belongs to the technical field of rail transit. The method comprises the following main steps: enablinga mobile ranging and dotting device with four ranging modules to move forwardly so as to acquire shape information of the vehicle body, fitting the central regression line of the vehicle body, enabling the mobile ranging and dotting device to move forwardly or reversely again along the central regression line so as to achieve dotting of the datum points and the like. Through the method and the system for measuring the datum points of the vehicle body, provided by the invention, automatic and intelligent measurement and dotting of the datum points of the vehicle body are achieved through the mobile ranging and dotting device with the four ranging modules, so that not only is the measurement accuracy of datum point improved, but also the efficiency of the datum point measurement is improved, the process time of the datum point measurement is shortened and the development of other subsequent processes is facilitated; meanwhile, the manpower required during the measurement is reduced, andthus the cost of measuring the datum points of the vehicle body is further reduced.