This article deals with systematics researches on the seed growth of maize grown in the variouscultivating densities with the methods of mathematics simulations and statistics analysis. The resultsare:the growth of maize seed has its own biological laws, and it is also controlled by environmentalconditions. The quantity of seeds is reduced several times in the growing process, and therefore thefinal quantity of effective seeds is only 50～74% of the total of the initial small flowers. The increases of seed weight and size and the accumulation of seed components tend to be a linear. Twothirds of the final accumulation depends on the effective grain-filling period. The seed yield is conditioned by final seed quantity and weight. Only improving the potential of seed quantity and weightcan a high yield be achieved.