The Chinese ever-ambitious project LAMOST (Large sky Area Multi-Object fibre Spectroscopic Telescope) has now come to its final completion of R&D stage. Major functions of the telescope have successfully passed a serial of pilot observation recently, and various kinds of applications integrated into the automation of the telescope chamber are being under vigorous site tests too. The TCS (Telescope Control System) is built on multi-layer distributed network platform with many sub-systems at different levels. How to efficiently process the enormous amount of message with particular implications running in and out the TCS is one of the major issues of the TCS software package. The paper focuses on the modelling of control system for LAMOST based on Petri net workflow. The model is also analyzed and verified with the matrix equation.