Carbon tax is an important policy instrument to control greenhouse gases. How to design a suitable carbon tax rate is of significance for policy makers. This study aims to address this issue from a microeconomic perspective by exploring the decision behavior of a potential investor. A trinomial tree model based on real options theory is presented to evaluate carbon capture and storage (CCS) investment in coal‐fired power plants considering uncertain factors. The model is then applied to a case study and the main findings are as follows: (1) carbon tax policy will have a positive effect on the CCS investment. If the carbon price is not high enough to trigger CCS investment, a hybrid mechanism integrating carbon trading and carbon tax to stimulate CCS investment is required; (2) in applying the trinomial tree real options model, the optimal carbon tax rate should be 145.3 RMB/ton for supercritical pulverized coal (SCPC) (or 79.54 RMB/ton for integrated gasification combined cycle (IGCC)) plants under current market condition and at current technological levels; (3) the optimal carbon tax rate is sensitive to uncertainties. Specifically, the optimal tax rate depends largely on not only the cost of the CCS investment but also the portfolio of carbon price volatility and the initial carbon price level. These conclusions provide the theoretical foundations for decision making regarding CCS investment and related policy making. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.