The present study demonstrates a construction procedure of a micro-photo bioreactor which has been used for the treatment of the simulated dairy wastewater (henceforth; SDW) by micro-algae chlorella vulgaris (C. Vulgaris). Moreover, this research is an experimental study in the laboratory scale and has been conducted in specific condition and parameters. Therefore, the effect of determined parameters such as flow rate, length of the micro-photo bio reactor, initial pH, luminous intensity and temperature on micro-algae has been studied. The obtained results from the SDW treatment by using specified micro-algae in the optimum situation illustrated that the removal efficiency of the chemical oxygen demand (henceforth; COD) in 120 working hours for flow rate, length of micro-photo bioreactor and the initial acidity, luminous intensity and the temperature effect is equal to 24.21% and 29.26% and 36.05% and 37.81%and 42.57%, respectively. The maximum percent of COD removal efficiency has been obtained in residence time of tau = 52 hours, and the optimum conditions of COD are equal to 42.57%. The turbidity value and existed TDS in SDW has been measured and compared together. Furthermore, significant differences were obtained from the analysis of each parameter. Consequently, the optimum concentration of micro-algae and the optimum pH for SDW purification was obtained (mi = 0.150 L) and (pHi, op = 8.00) on (COD), respectively. The purpose of this study is to evaluate the effects of micro-algae in COD removal from SDW by using C. Vulgaris micro-algae in the designed micro-photo bioreactor.