The competition for land resources created by the need for food security and ecological security is intensifying globally. To resolve the issue of land scarcity in agriculture following rapid urbanization, China implemented its requisition-compensation balance policy of cultivated lands in 1997, the introduction of which consumed numerous areas of land, such as river shoal and bare land, through reclamation. Moreover, these reclaimed and newly cultivated lands were mainly distributed in the northern part of China. Most previous studies of this subject have only examined the overall balance of cultivated lands in well-developed regions, and there is a lack of knowledge about the indigenous gains and losses before and after reclamation in important areas such as northeast China. Therefore, this study selected two representative county-level units in northeast China as the study area to analyze the conversion of cultivated land reserves during 1996-2015, evaluate the performance of reclaimed cultivated lands in terms of quality and productivity and calculate reclamation-induced changes in ecosystem service value. The results indicated that by 2015 only 16.02% of the original cultivated land reserves remained unconverted; nearly 60% were reclaimed as cultivated lands and over 20% were converted to other land resources. River shoal and ruderal land were the primary resources for cultivated lands compensation, and marsh, bare land and saline-alkaline land were found to be converted the most thoroughly. The gain of 23018.55 ha reclaimed cultivated lands were of relatively inferior quality and lower productivity, contributing approximately 4.32% of total grain output. However, this modest gain was at the expense of a 768.03 million yuan ecosystem services loss, with regulating services and supporting services being undermined the most. We argue that even if northeast China continues to shoulder the responsibility of compensating for a majority of cultivated land losses, it still needs to carefully process reclamation and introduce practical measures to protect indigenous ecosystems, in order to better serve the local residents and ensure prolonged food security with sustainability.