The integrated energy system (IES) is developing rapidly duo to its high energy efficiency and environmental protection. Environmental protection is an advantage of IES, and the costs of environmental externalities should be considered in the construction cost of IES in industrial parks. This paper considered the environmental externalities of coal, wind and photovoltaic power generation of industrial park IES (IP-IES) as a part of the unit cost of IP-IES, and constructed a capacity planning and optimization model, whose objective function is to minimize the cost per unit power generation. Subsequently, particle swarm optimization (PSO) is adopted into the model, and the model results are compared to the actual values, in order to determine the reasonable ratios of various types of capacity. Case study results show that: (1) considering environmental externality costs, photovoltaic and wind power have an advantage over thermal power. (2) Reasonable capacity planning can reduce the unit power generation cost. (c) 2020 Elsevier Ltd. All rights reserved.