Abstract: Explosion cases of small and medium-sized boilers were investigated and analyzed. A re-water test under the circumstance of boiler lacking water and an instability simulation test for circular furnace were conducted. Test analysis shows that main causes for boiler explosion accidents are lack of water and overpressure; the lack of water will cause an obvious degradation of boiler material performance, and the re-water will cause a sudden jump in boiler pressure due to sudden evaporation of water. With vertical boilers as an example, the explosion mechanism was presented. Finally, safety analysis was made on three types of boilers from the aspects of boiler structure, water capacity and safety accessories, and preventive measures were proposed accordingly.