Production plan is the most important part of the system of operational and strategic planning of the functioning of an industrial enterprise, since it affects almost all aspects of its activities. Moreover, a scientifically grounded optimal production plan provides a significant increase in the efficiency of the enterprise. The authors show that the production plan can be considered as an integral part of the business plan for the development of an enterprise with a wide range of activities and, in a narrower aspect, applicable only to production activities. The task of forming a production plan for one type of product (new or outdated) involves determining the volume of output of this product within a given period of time and given resources. More complex and, as a rule, existing in practice is the task of forming a production plan for the case when an enterprise simultaneously produces both innovative (new) and outdated products. The authors presented and formalized the task of forming a production plan for an industrial enterprise simultaneously supplying both innovative and outdated products. The authors' analysis of publications and research made it possible to establish the effectiveness of the use of linear programming tools to form a production plan for an enterprise. Respectively, the purpose of the study is to form an optimal production plan for an industrial enterprise and to study its stability with respect to various factors. In the article, in terms of linear programming, the basic mathematical model for the formation of a production plan for two types of products is presented. An example of calculating the scarce sections of a production plan in relation to the resources involved in the production and the available industrial capacities is demonstrated. It is shown that the use of estimates obtained in the formation of the optimal plan allows one to determine the boundaries of change in the parameters of the objective function, as well as the boundaries of error for resource-constraints, provided that the formed optimal structure of the production plan is preserved. In turn, this makes it possible to develop a production plan that is resistant to possible changes during its implementation. As directions for further research, the authors see the need to solve the problem of forming production plans for an industrial enterprise under the condition of a nonlinear objective function or model limitations.