The short circuit flow at the bottom of the vortex finder is an important factor for evaluating the performance of cyclone separators，but it is difficult to determine the altitude range of the short circuit flow.General measuring method is not available and the calculation results are quite different with various computation methods.Thus，to design a new separator many experiments are usually needed，which is time consuming and always costs too much.Here a computation method of short circuit flow based on CFD software is proposed.With the inflection point of the centripetal and centrifugal flow on the cross-section of the position at the bottom of the vortex finder，appropriate range for computing short circuit flow can be determined.The shape of the range is approximately annular and the descending flow rate across this range may be regarded as the total short circuit flow value.The calculation process is easily completed through the simulation result and the computation for short circuit flow is reliable.This method can be applied to multi-inlet and single-inlet separators.