Abstract: Due to the nature of absolute data, ecological footprint, capacity and deficit cannot be used to reflect and compare regional sustainable use level of arable lands. Based on the theory and method of ecological footprint (EF), productivity sustainability index (PSI) is developed as a new indicator for quantitative evaluation of sustainable use of arable lands. The index is the ratio of ecological capacity to the total of ecological capacity and footprint of arable lands in a region. This describes the level of regional land productivity supply meeting ecological contradictions between arable land supply and human demand. PSI is in the range of 0 to 1. A high index indicates high sustainable development of land use in a region and vice versa. A PSI of 0.5 implies marginal sustainable development. Hence the level of sustainability of a region can be evaluated based on the distance of PSI to 0.5. In this paper therefore, the results of a case study of Farm 45 Irrigation Area of the Xinjiang Production and Construction Corps for 1995~2005 show a weak sustainable level of arable land use for 1998~2003. The other years are simply not sustainable. This growth direction is not what we expect for ecological equilibrium. This shows that PSI is a more reasonable indicator than the absolute indicator of traditional sustainable level via ecological deficit.