In order to make a dynamic analysis of ecological capacity, to promote the sustainable development in the nature reserve, and to make Po-yang Lake Nature Reserve an example, the authors obtained information on the land use change in 1985, 1995, 2005 in Po-yang Lake Nature Reserve based on Remote Sensing (RS) and Geographic Information Systems (GIS). The ecological capacity were quantified using the ecological deficit and surplus by analyzing the development change, spatial characteristic, and the sustainable development status of the nature reserve. Results showed that the land use had been kept stable since the Po-yang Lake Nature Reserve came into existence in 1983. The change concentrated comparatively on grassland (increased 15.22%), water area (increased 7.05%) and unused land (decreased 18.19%). The ecological capacity improved from 1985 to 2005 (the ecological capacity from 0.8284 hm2/cap to 0.8568 hm2/cap to 1.0534 hm2/cap ). Among 9 villages and towns in the reserve, the ecological surplus villages and towns were Wucheng, Tiehe and Changyi, the ecological balance villages and towns were Sanjiao and Shahu, and others were in ecological deficit. In all of the nature reserve, the ecological capacity in the southeastern area was surplus but in contrast was deficit in the northwest. The degree of ecological harmony was 1.414, which proved that sustainable development in Po-yang Lake nature reserve was under sustainable status.