The invention provides a method for preparing an emulsified asphalt cold in-plant recycled mixture through two-grade design. The limitation of thought that the emulsified asphalt cold in-plant recycled mixture is prepared only through control of RAP grading in the prior art is broken through. By RAP and mineral aggregate two-grade design, the pavement performance of the cold recycled mixture is substantially improved. The prepared mixture has maximum density and splitting strength, and high-temperature stability and the pavement performance of the mixture are effectively improved.