A gas-solids fast separator was studied for its potential application in the process of coal pyrolysis to acetylene in plasma. The CFD method was employed to simulate the flow behavior in the gas-solids fast separator based on the realizable k-ε turbulence model and the discrete particle model（DPM）.The separation efficiency and residence time of gas phase in the gas-solids fast separator could be calculated. The numerical simulations were validated by the experimental results at a low velocity of the inlet gas（e. g. ，4 m·s-1）.With the increase of gas velocity at the inlet，the separation efficiency was increased，and the residence time of gas phase was reduced accordingly. The separation efficiency approached 100% when particle diameter was larger than 20 μm. When inlet velocity was 100 m·s-1，the mean residence time of gas phase was about 35 ms. To be noted，the performance of the gas-solids fast separator could be improved，for example by shortening the length of the separator，with a reduced residence time of gas phase at ～20 ms. It is expected that the gas-solids fast separator can meet the stringent demand of the coal pyrolysis to acetylene process for the milliseconds reaction，quench and separation.