The influence of two kinds of magnesium oxide expansive agent on self healing behavior of early concrete cracks under content of 5% and 10%(by mass, the same below) was compared and analyzed. The restrained expansion rate, crack morphology, crack width variation and recovery rate of compressive strength were tested. Results show that the higher the reactivity and the more the content of the magnesium oxide expansive agent, the higher the restrained expansion rate, and the better the self healing behavior of concrete cracks with the same initial width. In these experiments, magnesium oxide expansive agent has better self healing effect on early cracks with smaller initial width(less than 040mm), while the effect shows a significant reduction when initial width grows beyond 040mm. What is more, the 7,28d compressive strength recovery rate of the specimens mixed with magnesium oxide expansive agent will be significantly improved by 55%68% compared with the control group.