The invention, which belongs to the vehicle measurement field, relates to an apparatus and method for measuring a contour dimension of an automobile. The apparatus comprises X-direction adjusting rod assemblies, Y-direction adjusting rod assemblies, a Z-direction adjusting rod assembly, background plates, an X-direction datum line, a Y-direction datum line, and a computer. In addition, the method includes: calibrating a position; placing a to-be-measured vehicle in a measuring area and carrying out measurement, and displaying a vehicle measuring parameter on a screen of a computer. In order to overcome defects, the invention provides a reasonable measuring method to measure a main automobile dimension, so that an automobile needing measurement does not need to be parallel to measuring equipment absolutely; an error during measurement can be reduced and the read data become accurate; and the measurement time is short and the measurement efficiency is high. With a simple structure having advantages of easy installation and adjustment, the apparatus can be adjusted to reach a required state, automatic calculation can be realized, and the main dimension of an automobile can be displayed.