In order to study the influence of formulation factors on the performance of crumb rubber modified asphalt，resulting in optimizing the preparation formula，the factors of A（rubber powder source），B（rubber powder fineness）and C（rubber powder content）were selected to set the three levels. The softening point，ductility and viscosity of crumb rubber modified asphalt were used as evaluation indexes to optimize the formulation of crumb rubber modified asphalt by orthogonal test. The results show that，those factors have significant influence on softening point，ductility and viscosity. The impact on softening point can be described as：C>A>B，and the best level combination is A1B2C3. The impact on ductility can be described as：B>C>A，and the best level combination is A1B3C2. The impact on viscosity can be described as：C>B>A，and the best level combination is A1B2C2. The preferred combination scheme of different factors is determined as A1B2C2. Using this combination，the softening point of crumb rubber modified asphalt is 71℃，the ductility is 11.1 cm，and the viscosity is 3.0 Pa?s. The comprehensive performance of rubber modified asphalt is satisfactory.