The spread of pathogen particles emitting from the windows of infective patient room is studied by Lagrangian-Eulerian approach, hi this model, the continuous phase wind flow is simulated by the three-dimensional Reynolds-averaged Navier-Stokes equations coupled with RNG k - epsiv turbulence model and the dispersed phase pathogen particles are traced by Lagrangian model. The dispersed phase is injected from the window surface of patient room with a steady speed of 400 particles per second. By assuming no secondary infection, the concentration of pathogen around buildings is obtained. The present research is useful for forecasting and controlling the spread of airborne disease virus around buildings.