Two-Phase flow in stepped spillway is one of the most important criteria that must be investigated during the preparation of designs, as this characteristic is very important to avoid cavition in the stepped surface. The Bastor dam in the region of Iraqi Kurdistan,is one of the newly constructed dams. A mathematical model was made a full scale model using CFD to investigate the hydraulic conditions of the dam spillway for diffrent values of discharges. Mesh independnt solution is adopted to minimized the error. Volume of fraction is used to described the air water intrface. The mixing point of air and water was investigated and also the most at-risk areas for cavitation were identified. it can be noted that there is a negative pressure at the edge of firstly steps but cavitation does not occur due to low velocity which is lead to low dynamic forces. Also the location of the inception point of water starts at the steps number 17 and the percentage of air concentration reaches 90% starting from this point. Based on velocity distribution, cavitation level is variation on steppes number from (Steps 5 to 72), (Step1 to 22), (Step 1 to10) for flow rate 150, 250, and 313.15 m3/s, respectively. Based on cavitation index, cavitation level is variation on steppes number from (Step 26 to 72), (Step 13 to 33), (Step 5 to 14) for flow rate 150, 250, and 313.15 m3/s, respectively.