The present invention provides a method and an apparatus for determining separation efficiency of a cyclone separator. The method comprises: collecting solid particles separated by a cyclone separator; performing a particle size analysis for the collected solid particles; calculating feature parameters of the collected solid particles according to a result of the particle size analysis, wherein the feature parameters are values representing particle size and particle size uniformity of the solid particles; and determining a separation efficiency corresponding to the feature parameters of the collected solid particles as a separation efficiency of the cyclone separator, according to a predetermined correspondence between feature parameter and separation efficiency. The present invention avoids the difficulty in directly measuring the material concentrations at the inlet and the outlet of the cyclone separator and has a small interference with the apparatus. In addition, the test requires a simple operation and has a good repeatability.