Abstract. The percolation model was applied in the study of brittle to ductile transition (BDT) of polystyrene (PS) and polyolefin elastomer (POE) blends. Based on the interparticle distance and percolation model, stress volume (Vs) can be expressed by volume fraction (Vr) and ratio of the diameter of stress volume and the diameter of the domain (S/d). The percolation threshold (Vsc) varied from π/6 to 0.65. From the results of the Charpy impact strength of the blends, the percolation threshold for the brittle to ductile transition of PS/POE blend is 14 wt% POE, corresponding to Vsc≈0.5, which is consistent with the calculated value of π/6. Morphology observations show that the percolation point is correlated with the phase inversion of the blend.