Abstract: This paper presents three relations of the swirl coefficient of the flow in an S-shaped diffuser SC80 to parameters Vav, ΔCpbt1 and ΔCpbt2, respectively. Vav is the relative value of the average velocity of the flow at inlet section of the diffuser in vertical direction normalized by a reference velocity. ΔCpbt1 and ΔCpbt2 represent the differences of the static pressure coefficients between bottom and top walls at the inlet and at the end of the second bend of the diffuser. The analysis implies that the swirling flow in an S-shaped air intake could be monitored by a simple parameter.