The purpose of this study is to develop a semiconductor laser controlling system for photodynamic therapy(PDT) apparatus used with the second generation photosensitizer.The software system in personal digital assistant(PDA) supplies a controlling panel to control the whole system by parallel interface in PDA,which is designed by VC6.0 language.The results show that a PDT instrument with the above system works steadily.The controlling system has the characters of portable,convenient,inexpensive,rapid and precision.