In China, the pattern of farmland use has been greatly changed due to the rapid development of the economy, since economic reform in 1978. Variations in available farmland, in terms of both quantity and quality, have brought about changes in grain production. This paper analyzes the spatiotemporal pattern of China' s level of farmland use for the period 1978 to 2004, and develops a “farmland—grain elasticity coefficient” (FGEC) to reflect the interrelationship between changes in farmland use and levels of grain production, using agricultural statistical data from local governments. The outcome of this study indicates that since 1978 the effect of farmland loss on grain security has been somewhat abated, due to increased investments and the subsequent improvements on farmland. Since the initiation of economic reform, China' s level of farmland use has been generally improved. These improvements are mainly due to rapid economic development and constitute a move across a gradient from the southeast coast of China to the Chinese inland areas, following the same path as that of economic development. However, continuous improvements in the level of farmland use may not always bring about sustainable and steady growth in grain output. Therefore, considering the law of diminishing marginal utility, in developing countries, the area of available farmland will play a key role in maintaining security in grain production. This will also constitute a practical scientific basis for strict farmland protection objectives and strategies for China.