Abstract: With the molten paraffin applied to simulating the cold air quenching for the granulation of liquid steel slag in lab, the effects of gas pressure, airflow velocity, gas flowrates and liquid steel slag flow and its vertical falling distance on the granulation were investigated. The results showed that after the granulation the distribution of paraffin grain size is in inverse proportion to the gas pressure/flowrates and airflow velocity. Based on the similarity principle and dimensional analysis, the criterion was given correspondingly. Then the air quenched paraffin and granulation was calculated and the results revealed that the grain size of granulated steel slag is relatively even and all grain sizes are less than 3 mm if the gas pressure p=0.56 MPa, airflow velocity v=93.33 m/s, vertical falling distance l=18.7 cm, and gas flowrate Q=338 m³/h. The parameters as above are available to the in-situ granulation of liquid steel slag for reference.