Abstract: The number of Al type inclusions was analyzed by original position statistic distribution analysis(OPA) and the three-dimensional morphologies of inclusions were observed by a special depth erosion method.Total oxygen and nitrogen during the refining process were determined.Cleanness changes of the steel were evaluated by prolonging the RH pure circulation time.It is shown that the total oxygen can be reduced to 30×10^-6 when the RH pure circulation time is 8 to 10min after alloying;the scrap steel should be adjusted before adding Al or titanium alloys,or it can influence the cleanness of the steel.The number of inclusions reaches the maximum value of 7.02mm^-2 after adding Al within 5min,with the main inclusions of cluster Al₂O₃,and the size and number of inclusions decrease significantly during RH pure circulation after alloying.