We used Monte Carlo method and considered the additional heat generated by solar radiation to establish the CFD models of the Office, which based on Reynolds-averaged equations and two equation k-εturbulence. It studied the velocity distribution, temperature fields, PMV value and PM2.5 concentration fields in the Office. Calculation results and experimental data show that: the simulation model can accurately calculate the indoor thermal environment. The diffuser is not reasonable and the wind speed distribution is uneven. They cause the PMV value is big and we will feel hot. So it needs to further optimize the wind outlet or opening size. The average indoor temperature is at 26.15 degrees. It is uniform no more than plus or minus 2 degrees.But the heat emitted from the computer, human body and fluorescent lamps have influenced the temperature field distribution nearby. The content of PM2.5 is good and the fine particles on the surface of the indoor article have a certain influence on the concentration of PM2.5.