Abstract: Diatomite was used as modifier to prepare diatomite-modified asphalt at different contents. The modification process and mechanism of diatomite modified asphalt were characterized by IR, SEM, OM, and a model diagram of the modification process was inferred based on the analytical results of IR, SEM and four components of asphalt. Furthermore, related performance of the diatomite-modified asphalt was examined with TG, penetration, softening point, ductility test, respectively. The results show that diatomite modified asphalt exhibits no obvious chemical change, it is showed that diatomite absorbed asphalt physically, solvent components of relatively strong liquidity and smaller molecular weight in asphalt are easily absorbed into or around diatomite for its porosity and large specific surface, they can be congealed and hardened to form a stable and homogeneous lump with diatomite when temperature decrease. This is the main reason for improvement of high temperature performance of diatomite modified asphalt. The content of diatomite is not positively related to the performance of modified asphalt. The temperature sensitivity and low temperature performance of the modified asphalt will be worse with increase content of the diatomite, the global performance of diatomite-modified asphalt is relatively good when the content is 13%.