This paper develops a mathematical model to investigate the performance of a modified solar chimney power plant (MSCPP) for purposes of both power generation and vegetation. It then estimates the net added benefit. Results show that with the vegetation area enlarging, the mass flow rate (MFR) of the vapor increases, and more heat is used as the latent heat for water evaporation, leading to considerable reduction of the power. Vapor condensation from the saturated air occurs only for very large vegetation area. On a cooler day, the plant produces less power and the condensation occurs for smaller vegetation area. Higher relative humidity of ambient air results in clear reduction of the MFR of the vapor evaporating from the vegetation area, and accordingly the great enhancement of the power. The benefit from agricultural products is larger than the benefit loss caused by the electricity loss, and the benefit of fresh water condensed from the saturated air is negligible. This leads to the benefit increase for the MSCPP compared to the conventional plant. The benefit increase becomes greater with larger vegetation area. When the chimney is heightened from 1000 m to 1500 m, the power is greatly enhanced; however, the net added benefit becomes smaller. (C) 2019 Elsevier Ltd. All rights reserved.