A system is developed to measuer the threshold current of semianductor laser.The system is based on Single Chip Microcomputer (SCM) and Virtual Instrument (VI) technology.Driver for semiconductor laser,control and sampling circuit were developed.With the VI technology,commuiction between test unit and process and control unit (PC) is realized.PC is used to set up the test current,process the measured data sent by the SCM.Three kinds of processing method were programed and tested.Results show that the bi-linear fit method has the most accuracy and the best stability to determine the threshold curent.