Abstract: With the continuous development of unconventional oil-gas reservoirs, it has been quite difficult for the traditional Arps decline equation to describe the production decline process of large-scale volume fracturing and horizontal wells in unconventional oil-gas reservoirs. Therefore, by summarizing and studying the mathematical model of the existing production decline equation, the observation time in Arps production decline differential equation is replaced by a composite function that has time attribute and reflects the development and change of oil-gas reservoir system, and a general production decline equation with more general adaptability has been established. Under certain conditions, this general equation can be transformed into various existing common production decline equations, and also form new high-precision production decline equations. It is expected that in the future, the research of production decline equation will mainly focus on the determination of the relationship between composite function and decline time. Once the new relationship between composite function and decline time is determined, a new production decline equation can be formed. Meanwhile, for the convenience of application, the paper systematically provides the calculation method of the general production decline equation under the condition of two kinds of relationship between composite function and decline time. Through practical applications, it has been found that it is highly effective to use the time-varying structure estimation method and perform fitting between the general equation of production decline when T=mt^b and the production decline curve of unconventional oil reservoirs in Ma 56 wellblock, and the estimated production is very close to the actual value.