In order to reveal the modification mechanism of But on Rock Asphalt(BRA)，through separating with extraction and combustion as well as the material physicochemical and microscopic experiments， the properties of raw material， mineral， pure natural asphalt and modified asphalt of BRA were analyzed to compare with that of mineral powder and or-dinary road petroleum asphalt.The results show that the BRA mineral is large in specific surface area with porous limestone structure， and it can be used as the mineral powder.The pure asphalt of BRA belongs to the hard natural asphalt， and it is high in asphalt en econ-tents， more in aromatic ring structure contents and big in molecular weight of asphalt ene and colloid.Furthermore， N， Sand other miscellaneous elements exist in the form of func-tional groups， stable in colloids and poor in rheological characteristics.There are very strong effects of wrapping and adsorption between the pure asphalt and the mineral of BRA to form as table granular structure.At the sametime， the compati bit ity is good between the pure asphalt of BRA and the petroleum asphalt with highly stable physical fusion to make that the BRA is able to inherit its excellent properties to the petroleum asphalt.Therefore，mixing the BRAin to the petroleum asphalt， its modification mechanism is mainly the tack i-fying effect of natural hard asphalt and the strengthening effect of limestone mineral， so it can effectively improve the resistances to high temperature， stripping， deformation， ageing and temperature sensitivity etc.， and it is a kind of excellent pavement modifier.