The paper presents an advanced technique, SHG-FROG (second harmonic generation frequency-resolved optical gating) to measure an ultrashort laser pulse. The computer is programed lo retrieve the amplitude and phase of the pulse. The retrieved results got by the program and the development of the traditional algorithm and experience and rule to use the algorithm practically are given. Not only was the FROG method tested to be easily built up but also the algorithm is handy and quick.