The invention discloses a determining method of soot capturing efficiency of a kitchen ventilator based on CFD. The determining method comprises the steps of firstly outputting a distribution histogram of the occupation ratio of the particle standing time to particles of each boundary face for the internal face of the kitchen ventilator; secondly, defining the particles as primary capturing particles or secondary capturing particles; finally, counting and recording the primary capturing particles and the second capturing particles of all wall faces inside the kitchen ventilator respectively; calculating the capturing efficiency. Compared with the prior art, in CFD numerical value simulation study, the operation is convenient, the indoor motion of soot particles is more precisely simulated,the primary soot capturing efficiency and the secondary capturing efficiency are more quickly obtained, the time wasted in calculation and the calculation memory space are greatly saved, and the study period is shortened.