The development of a simulation model of an extensive pastoral farming system to assist analysts in their assessment of government policy measures is described. The model was designed to simulate, over a number of years, the physical and financial operation of a sheep and beef production system typically found in the North Island hill country of New Zealand. By manipulating model parameters and data related to prices, costs, taxation and credit, a range of policies can be represented and their effects simulated. The model is used to undertake an ex post analysis of the farm-level impact of the supplementary minimum price scheme in New Zealand and to project farm performance following the abolition of the scheme. Consideration is given to the use of the model to represent sheep and beef production systems elsewhere.