Teacher Cheng-En Li has participated in many research projects, mainly divided into two categories: academic research and practical applied research. Academic research, such as the population structure study of brown tree frogs he conducted while in graduate school, involves weekly surveys in the Shuangxi and Gongliao areas of the northeastern Taiwan, records frog numbers, studies population dynamics, and examines the relationship between weather and the environment. Applied research includes projects for government agencies, such as investigating the impact of engineering projects on frogs or exploring solutions to improve the current plight of frog conservation. He employs different research methods for different research purposes, including field surveys of amphibian species and numbers, recording, and even DNA analysis.