Polystyrene /active Talc ( PS /Talc) composites were prepared by means of a parallel triple-screw extruder with excellent mixing ability. Then, the dispersion of Talc in PS matrix was analyzed, and the mechanical properties and thermal stability of PS /Talc composites were investigated. Meanwhile, the key factors affecting cell structure were discussed via extrusion foaming orthogonal experiments. The results show that (1) the dispersion of Talc in PS matrix is improved by the triple screw extruder, and Talc can be dispersed in PS matrix evenly when the Talc content is below 6%; (2) the tensile strength, the impact strength and the elongation at break first increase and then decrease as the Talc content reduces, and they all reach the maximum when the Talc content is 6%; (3) with the increase of the Talc content, the flexural strength decreases while the flexural modulus increases; (4) the addition of Talc can enhance the thermal stability of PS /Talc composites, and the thermal stability reaches the maximum at the Talc content of 10%; (5) the primary factor affecting the foaming behavior of PS /Talc composites is the Talc content, which is followed by the die pressure and the die temperature; and (6) when the Talc content is 8%, the minimum cell size and the maximum cell density are obtained, which are 12.4μm and 2.4 × 10⁸ cells /cm³ ,respectively.