Abstarct: One of the fundamental parameters of perturbative QCD is the coupling . In this thesis, the theoretical basics of the coupling parameter of strong interactions are reviewed. In electron-positron annihilation coupling constant is determined using three and four jet rates and so with applying the perturbative expansion at NLO and NNLO approximations. It Furthermore, is performed computing for coupling constant at reference scale boson Z0 mass in four energies from OPAL detector and computing optimized renormalization scale factor for 91GeV energy.