In order to resolve the problem encountered in industrial applications where the object to be measured is longer than that of the laser beam used as datum, a laser relay measuring method was proposed. In this method, the object was divided into several segments and each of them was measured separately. There is a superposition part of a certain length between two adjacent segments. Based on the measured results of this superposition part in two separate measurements, the relation of the two coordinate systems was found with least square method. All data measured separately could be expressed in a unified coordinate system. The method, used for straight line type object to be measured as an example, was presented in details. Its error was analyzed and the method for selecting parameters in the laser relay measuring method was given according to measurement accuracy requirement. Factors influencing the measured results were discussed with an industrial application example. This method was used in track geometry surveying of railway for passenger dedicated line, getting satisfactory results.