Wildfire is an important factor in the evolution of terrestrial organisms, and fires assist in maintaining the structure and function of the global ecosystem. Knowledge of fire severity is indispensable for understanding the ecological significance of wildfire. Therefore, quantifying fire severity is an important aspect of studying the response mechanism of terrestrial ecosystems to wildfire, and it is of great significance to fire ecology. In this paper we comprehensively introduce and compare the classification and quantification methods for fire severity; we discuss the development and application status of various methods, and we elucidate their existing problems. We analyze each method in terms of the relevant ecosystem, the fire behavior, time, and the relationship between fire severity and ecosystem response in order to provide a reference basis for proposing and developing new severity measurement methods. The current methods for describing fire severity include four main types: 1) According to features of the burned area, fire severity can be classified as light, moderate, and heavy. 2) Using composite burn index (CBI) to quantify and record the fire severity. 3) In quantifying fire severity with vegetation change, there are certain limitations and theoretical problems to be solved. 4) Remote sensing could very well be an important means of measuring fire severity in the future, but there are still many problems that need to be solved before the remote sensing index can become a global fire severity indicator. Fire severity is a latent variable in ecosystem. Only by clarifying the relationship between fire behavior, fire severity, time related variables and the pre-and post-fire ecosystem can the existing models be perfected or new, better fire severity measurement models be proposed for broad applications.