From the development history of ecology, the first is the field research method. For example, to understand the changes of animal populations, we must first observe and collect data in nature. The field and experimental laboratory were separated in the 1920s. An effective auxiliary means to analyze causality in laboratory. The most commonly used methods to study simulation theory by using mathematical models. Only by obtaining experimental items and data from the field and returning to the laboratory to repeat the experiment indoors can we get some rules, and consolidate this result through modeling and make predictions. The parameters can also be changed appropriately, so that the research of mathematical model is gradually close to reality.