The article is devoted to the study of the features of the life cycle of an ecological system project, the functioning of which is based on the principles of circular economy as a modern economic model that allows achieving the goals of sustainable development. The relevance of the presented research is confirmed by the need to take into account the eco-destructive impact on the environment in the implementation of economic activities, since the technogenic linear type of economy created over the past centuries has led to an environmental crisis and turned out to be unable to ensure balanced civilizational development without damage to the environment. The issues of the structure of the life cycle of an ecological system project are considered, which takes into account the ecological orientation of this type of projects. It is proposed to include five phases in the life cycle of an ecological system project: pre-investment, investment, operational, regenerative and revitalization, which are divided into stages during which the intermediate result of the project is created. Using the tools of category theory, a graphical model of the project life cycle was created, in which successive and overlapping links are established between phases. The links between the stages of the life cycle are analyzed, represented by objects (domains and codomains) and morphisms (sequential and parallel, incoming and outgoing) of the category «Life Cycle of an Ecological System Project». The relationship between the duration of stages of the same or different phases of the project life cycle has been determined. The time parameters of the phases, stages and time intervals of the project life cycle have been determined. A mathematical model of the life cycle of an ecological system project is presented for two options for determining the duration of the life cycle: strictly and loosely defined. A compensation mechanism has been proposed to stabilize the life cycle duration in the case of its strict definition, which provides for the adjustment of the duration of codomains in certain morphisms of the category.