Global warming is a challenge and threat for human beings. As a rising power, China has its own obligation to contribute to emission reduction which is also a requirement of sustainable development. CCS technology plays an important role in emission reduction for its ability to achieve large amount of reduction in a short time. CCS investment is full of uncertainty, the investors have flexibility during the process. In this paper, the characteristics of CCS investment was taken into account, and the investment decision model of CCS investment was build. Researches show that policy on CO_2 emission is a key factor of CCS project investment decision. In this study,carbon tax rate is set as policy variable. Function of project value of CCS is given, which take the value of real option into consideration. Under the assumption that as long as the tax rate is able to make manufacturers to invest in CCS, the policy is effective and the smallest effective rate is the best rate which gives manufacturers more profit, the model is solved according to the critical condition that value function of CCS equals to zero. As a result,an implicit function of parameters a critical tax rate is derived. In the last part of the study,sensitive analysis is done using numerical simulation. The effectiveness of carbon tax policy is found to be highly influenced by carbon price, risk free rate and the amount of investment. Policy strategy is recommended according to the findings.