Based on GABLS2 (the 2nd case of Global Energy and Water Cycle Experiment Atmospheric Boundary Layer Study), a SCM (Single Column Model) experiment is constructed to evaluate the diurnal cycle of PBL (Planetary Boundary Layer) processes in GRAPES（Global and Regional Assimilation and PrEdiction System）. Compared with observation and LES (Large Eddy Simulation), GRAPES simulates the 2m temperature reasonably with the prescribed surface temperature forcing. However, it is found that the simulated downward sensible heat flux，10m wind speed, surface friction velocity, and PBL height are overestimated under stable condition (during nighttime), while the simulated upward sensible heat flux and PBL height are underestimated under unstable condition (during daytime). Sensitivity experiment shows that the simulated 10m wind speed and friction velocity in the stable boundary layer, as well as the profiles of wind and temperature in the convective boundary layer, are closer to LES if the background diffusion values are reduced.