In order to study the evolution law of yield heterosis of different era maize variety in north China andprovide theoretical basis for the improvement of maize varieties, the evolution characteristics of yield heterosis inthe process of maize variety replacement in north China were compared and analyzed under the three planting densi-ties using the large-area popularization single-cross maize variety and their parents of 1970 s, 1980 s, 1990 s and2000s in north China were used as experimental materials. The ...