Food security is guaranteed only when unexpected shocks, e.g., epidemics, economic crises, and extreme climates can be well responded to the stable food supply. Food stability, which is not exclusive of the status that we have enough food stock to satisfy a population's food demand to avoid people from hunger for a certain period until the regular food supply recovers, has never been quantified. Here, we propose a new metric, the ratio of stock to demand, to quantify how domestic food consumption need of a population can be satisfied by the domestic food stock. This study collects the data available for 117 economies from 1991 to 2018 to analyze the grain stock-demand ratio (GSDR) and its determinants of the world. In terms of GSDR, global food stability has increased. In particular, the increased stability found expression in Asia and Africa. The increased stability was mainly driven by the growth of grain stock-production ratio (GSPR) and grain cropping yield (GCY) most significantly from 2000 to 2010 and the decrease of average labor input in unit agricultural land (ALI) majorly from 1991 to 2000. Meanwhile, GSDR was pulled down significantly by the sharp fall of grain crop land (% of total agricultural land) (GCL) from the year 1991 to 2000 and continuous decrease of employment in agriculture (% of total employment) (EIA) particularly from 2000 to 2018. Based on the results, policy suggestions are proposed towards sustainable development goal 2 (Zero Hunger).