This paper describes the system modelling, architecture design and implementation of the observatory control system (OCS) of the LAMOST (Large Area Multi-Object Fibre Spectroscopic Telescope). The software-reuse technique, object-oriented technique, component and framework based software-developing methodology are used in the system architecture and implementation. The architecture of OCS is established based on a component-based layered system using many patterns such as the MVC (Model/View/Controller) and proxy. For the effective and safe exchange of commands and status between OCS and the subsystem, a unified message bus is defined and three protocols, namely a command acceptance/rejection protocol, a command execution feedback protocol and a status handling protocol, are proposed. The interface protocol between all the subsystems is defined. The full utilization of advanced computer technologies including the database, distributed computing, real-time computing, standard data exchange and expert system technologies has benefited the OCS software development. This paper describes the system modeling, architecture design and implementation of the observatory control system (OCS) of the LAMOST (Large Area Multi-Object Fiber Spectroscopic Telescope). The software-reuse technique, object-oriented technique, component and framework based software- developing methodology are used in the system architecture and implementation. The architecture of OCS is established based on a component-based layered system using many patterns such as the MVC (Model / View / Controller) and proxy. For the effective and safe exchange of commands and status between OCS and the subsystem, a unified message bus is defined and three protocols, ie a command acceptance / rejection protocol, a command execution feedback protocol and a status handling protocol, are proposed. The interface protocol between all the subsystems is defined. The full utilization of advanced computer technologies includes the database, distributed computing, real-time computing, standard data excha nge and expert system technologies has benefited the OCS software development.