Based on functional analysis of cold patching asphalt mixtures, an additive for cold patching asphalt was synthesized with vinyl siloxane, unsaturated fatty acid, alcohol wetting agent and other basic materials and its improvement effect was evaluated by FTIR and DSC analysis. This additive was used for modification of mastic asphalt along with diesel as diluent under specific processing, and the formulation of cold patchping asphalt was decided based on the Brookfield viscosity test and adhesion test. Three kinds of cold-filled asphalt mixture grading were designed. The optimum aggregate gradation was selected and performance of cold patchping asphalt was evaluated by mixing test, adhesion test, cohesion test and indirect tensile strength test of the cold patching asphalt mixture. Results shows that the content of diesel has more visible effect on viscosity of liquid cold patching asphalt than that of additive, cold-filled asphalt mixture is suitable for coarser grading, temperature stability of liquid cold patching asphalt, adhesion of liquid cold patching asphalt to aggregate, indirect tensile strength and cohesion of cold patching asphalt mixture increase significantly with the addition of additive. The suggested mass ratio of matrix asphalt and diluent ranges from 79:21 to 77:23, and the mixing amount of auxiliary additive is 3%. The optimum binder content of cold patching asphalt mixture containing cold patch asphalt is 4.7%-5.0% by mass.