Petri Net is an important model to discribe and analyse dynamic features of cocurrent systems. With further research of Petri Net theory and application to various practical areas, it is necessary to develop CAD tools which can support design and analysis of Petri Net. GPNT (Graphic Petri Net Tools) is a Petri Net tool made by Computer Science Department of Northwest University of China. It is used to assist the design, dynamic simulation and analysis of P/T Net. This paper briefly introduces the functions of GPNT and discusses some technical problems in the design and implementation of it.