Completely understanding the conditions and mechanisms of deep moist convection (commonly referred to as “thunderstorm” in operational forecasting) and severe convective weather (especially tornadoes) is the basis for better forecasting them. This paper first analyzes the relationships between convective available potential energy and convective inhibition energy and temperature and humidity of lifted air parcel, physical significance of convection temperature, and water vapor amounts for deep moist convection, and then further proposes the definition of significant severe convective weather in China, presenting some spatiotemporal characteristics of severe convective weather, the relationship between extreme rainfall and surface dew point temperature, the producing mechanism of convectively high winds, the physical significance of wet bulb temperature closely related to hail melting layer, the environmental conditions for supercell storms and tornadoes, and the formation mechanism of mesocyclones and tornadoes. Finally, understandings of vorticity and hodograph, and their relationship with mesocyclones and tornadoes are given. Different interpretations and threshold values of some concepts and variables listed in this paper and our understandings are provided for readers to study and compare.