Type Ⅰ and type Ⅱ waste plastic modified asphalts were prepared by type Ⅰ waste plastic modifier（made by granulating process） and type Ⅱ waste plastic modifier（made by heating and adding stabilizer process） respectively. The storage stability, softening point and low temperature performance of type Ⅰ and type Ⅱ waste plastic modified asphalts were tested. The Marshall stability and high temperature stability of type Ⅰ and type Ⅱ waste plastic modified asphalt mixture were tested. The molecular structure difference between type Ⅰ and type Ⅱ waste plastic modifier were studied,the mechanism for waste plastic modifier modifying asphalt was investigated. The results show that the softening point of type Ⅱ waste plastic modified asphalt can be up to 60℃ and the difference of softening point between the upper and lower layer of sample is less than 25℃. The Marshall stability of type Ⅱ waste plastic modified asphalt mixture is better than that of type Ⅰ waste plastic modified asphalt mixture in general. Compared with type Ⅰ waste plastics modifier, type Ⅱ waste plastics modifier has shorter molecular chain, more side chain and more double bond, and has —OH group in the molecule. There are no new substances in two types of waste plastics modified asphalt. It is proved that the construction process of Ⅱ B waste plastics modified asphalt is similar with SBS modified asphalt and the pavement situation is favorable at present. The Ⅱ B waste plastic modified asphalt mixture can be used as the surface layer and underlying layer of pavement.