At present, to improve the performance and extend service life of asphalt pavement and decrease the damage caused by all kinds of environmental change, road researchers are world widely interested to produce high quality modified asphalt and have done some tentative research. This paper mainly researches on the character of asphalt and the mechanism of high polymer modified asphalt by the analysis of molecule structure 、physical structure 、 composition of asphalt and modified mechanism of high polymer modified asphalt.1 、 According to the different status and performance of asphalt in different environmental temperature, through the analysis of GPC、DMA and IR, a new point about the structure of molecule and solidity of structure has been put forward in this paper. Expatiating the relationship between the asphalt physical structure in the theory of molecular movement.2、 Through the GPC analysis, the result has shown that we can't divide the similar chemistry character of proportion into the same group, so this paper put forward a new method to divide the composition of asphalt in pavement by TG Analysis.3、Due to the asphalt is sensitive to the environmental temperature, there is no systemic separation section to describe the sticky elasticity of asphalt. This paper put forward the new method and new theory of dividing the asphalt into glass form、high elasticity form and viscidity form.4、 With the common SBR and SBS modified agent, through the TG、 DMA、 BBR、 elastic reversion、 DSR and revolving viscidity experiment, this paper has studied on the how the modified agent influence on the character of asphalt and put forward a new point of modified mechanism of high polymer modified asphalt in the angle of molecular thermal movement.