Push off tests for high strength concrete(HSC) specimens after elevated temperatures were carried out to study the effect of elevated temperature and concrete compressive strength on shear strength of HSC. Based on the variation of the meso structure of HSC shear plane, the mechanism for shear strength change of HSC after elevated temperatures was investigated. The relationship between aggregate fracture rate and shear strength of HSC after elevated temperatures was discussed. Results show that when the compressive strengths are 647,940MPa at room temperature, the shear strengths of HSC after 200℃ have a little decrease and a little increase compared with that at room temperature, respectively. When the elevated temperature exceeds 200℃, the shear strength of HSC reduces with the increase of the elevated temperature. The higher the compressive strength of concrete (at any temperature) is, the greater the shear strength will be. The aggregate fracture rate of HSC shear plane decreases as the elevated temperature rises and it will increase as the concrete compressive strength increases. At last, the aggregate interlock model for HSC after elevated temperatures is proposed.