The structure of the traditional grating projection system is difficult to construct for its rigid geometry constraints. In addition, the reference plane is inevitably employed in the system which limits the range of the measurement and the application. In order to resolve the above problems, an assistant line is introduced to the system. The equation of translation from relative phase to absolute phase is deduced according to the assistant line. Space mapping method and its optimization algorithm are employed, by which the object′s real 3D data can be calculated. A circle liner target is designed, with which the extraction of feature points, target phase and feature line can be accomplished by only one image, and the procedure of the calibration is simplified. Last, the profile of a plaster model is measured by the system with two images, and the accuracy of the result is proved, the mean-square deviation (MSE) of the distance between ten shifting planes is 0.02 mm, and the MSE of the angle between ten rotating planes is 0.03°. The experiment shows that the method is accurate, fast, and easy to construct and calibrate, which has improtant application values.