Although the interest rate has been adjusted down several times, deflation still exists, so investment evaluation becomes more difficult. Under such economic environment, as to break-even analysis the effects of interest rate and deflation should not be ignored while in the conventional model the two factors are usually unconsidered. The break-even point may move and the reliability of investment evaluation may be affected due to these factors. In the paper the conventional model is improved by introducing the factors of interest rate and deflation and some new results are presented.