As the number of cores integrated on system-on-chip(SoC) increases continually, energy reduction technology is becoming an important challenge. Dynamic voltage and frequency scaling(DVFS) is one of strong low power techniques in SoC design. In this paper, we propose a slack-distribution based DVFS technique using the characteristics of tasks in multi-processor SoC (MPSoC) environment. Also, to utilize slack-time effectively, we determine the order of all task paths depending on power-weight. Experimental results show that the proposed technique can reduce energy consumption by 11.6% when compared to existing methods.