An optical tehcnique for 3 D shape measurement is set up.The technique,based on a deformed projected grating pattern which carries the 3 D information of the measured object,can automatically and accurately obtain the phase map of a measured object by using a liner phase FIR filter.In contrast to the 2 D FFT technique,the technique is much faster.Only one image pattern is sufficient for measuring.The phase map can be processed without assigning fringe orders and making distinction between a depression and an elevation.Theroetical analysis and experimental result are presented.