In recent years, the requirements of the high spatial resolution and dE/dx for the flavor, Z pole, and Higgs physics in the high-energy physics have been raised. To meet this requirements, the design of high-energy e+e- colliders has been improved the very high luminosity to Tera Z. The Circular Electron Positron Collider (CEPC) is a proposed high-luminosity factory for Higgs and Z pole run, with a the maxim luminosity of $10^{36}cm^{-2}s^{-1}$. Time Projection Chamber (TPC) is an important detector option for tracking in e$^+$e$^-$ collider, which included the high spatial resolution and excellent particle identification (PID) resolution. The Pixel readout TPC technology, known for its low material budget, high occupancy, and good PID capabilities, is developed as a promising option at the Tera Z comparing the classical pad readout TPC technology. By the utilizing cluster counting, the pixel readout can significantly enhance PID resolution. The simulation studies are ongoing at Institute of High Energy Physics, CAS to improve detector performance at the different granularity readout. This paper presents the structure of the pixel readout TPC simulation framework and some preliminary results. The simulation results demonstrate the optimization of the high-granularity readout
($300\,\mu m\sim500\,\mu m$).