The investment in human capital is irrevocable, and the principal investor is able to decide the timing of investment, therefore, it is necessary to introduce a model of real option theory into the human capital investment. The existing research is participating of the assumption that work is irrevocable, while its conclusions are based on the fact that non-monetary income is tax-free. However, it is considered that the research object should be the investment ineducation by the investor rather than participation in the work； the sinking costs of education investment include increasing education fee and abandoned labor income that are both subject to the tax rate change. The results show thatthe existence of the real option value makesindividuals invest in higher education even more hesitant, as a result that theyneed to increase the required return on investment. In addition, the existence of the real option value would reduce the influence of investment return on human capital. Furthermore, the tax rate will affect the investment costs, thereby will affect investment decisions.