In recent years, the study of active particles has become one of the important topics of concern for researchers in many fields, among which the phase separation of active chiral particles has important theoretical and practical significance. This paper investigates the phase separation of binary mixed systems composed of active chiral particles with different diffusion coefficients through Langevin dynamics. A smaller relative diffusion coefficient is conducive to the formation of large clusters and separation of "cold" particles, while a larger relative diffusion coefficient will weaken the separation effect. Due to the influence of particle characteristics (self-driven velocity, self-rotational angular velocity) and relative diffusion coefficient on the collision between particles, if one wants the "cold" and "hot" particles to reach phase separation, the increase (or decrease) of self-driven velocity and self-rotational angular velocity cannot be synchronous, and the relative rate of change of self-driven velocity is smaller than that of the self-rotational angular velocity. By analyzing the changes of the effective diffusion coefficient of "cold" particles, the phenomenon of phase separation in the system can be better explained. A smaller effective diffusion coefficient means "cold" particles will aggregate into larger clusters, and the system may exhibit phase separation. However, when the effective diffusion coefficient is larger, the diffusion of "cold" particles is stronger and the "cold" particles will not form large clusters, which means the system could not aggregate into phase separation. In addition, with the filling rate of particle increases, the proportion curve of the number of cold particles in maximum cold particle cluster undergoes a non-monotonic change, which is first increasing and then decreasing, and each curve has an optimal filling rate with different widths.With the increase of the relative diffusion coefficient and self-driven velocity, the width of the optimal filling rate of the proportion curve will become narrower and shift to the right.