Based on the functional approximation of a target volume DVH (TV-DVH) to a modified step function, we propose a new index that indicates the degrees of dose coverage and homogeneity for target volume reached in clinical routines. Forty-seven IMRT patient plans are included in the analysis to explore the efficiency of the proposed method. The new index, named s-index, was defined to vary from 0:05 for clinically acceptable TV-DVH at our institution and showed the ability to give the user an idea whether the degree of dose coverage and homogeneity for target volume were adequate when the user-defined criteria had been in place. The result shows that the lower value of s-index indecates the higher dose coverage for the tumor volume and/or the higher dose homogeneity showing the faster fall-off rate at the percentage dose higher than 100%. In addition to the quantification of dose coverage and homogeneity is has been also shown that s-index is more accurate in evaluating the dose homogeneity in tumor volume than the conventional method. The proposed method has demonstrated the effectiveness in evaluating TV-DVH in terms of simple index and supplements currently used indices by providing complete information of a DVH curve in a treatment plan.