This study was undertaken in an area of Bangladesh to assess the impact of minor irrigation on different farm sizes and determines the optimum allocation of resources of large and small farmers among different crops in a shallow tubewell (STW) irrigation system. Farm survey method was used to collect data in order to develop linear programming representative farm models. The analysis takes into account crop activities, inputs used, farm size and soil types. Optimal plans show mis-allocation of existing resources and indicated considerable scope for increasing farm income by reallocation of existing resources. The mis-allocation of resources on large farms was greater than on small farms. The analysis suggests that, by reallocating existing resources, large farms can increase farm income and employment more significantly than small farms. The research supports the view that the government should maintain a policy that favours private sector investment and operation of STW irrigation and the extension workers may direct farmers to allocate their resources in better way.