Radiosonde (RS) data over Beijing in 2008 was employed to analyze vertical distributions of water vapor in this area. A parameterization scheme of water vapor profiles is proposed according to different conditions of Planetary Boundary Layer (PBL). In the condition of Stable Boundary Layer (SBL) or shallow boundary layer, the parameterization scheme of water vapor profiles can be formulated by q=q₀e^z/2624, here q₀ is specific humidity at surface. In the condition of Convective Boundary Layer (CBL), the vertical distribution of water vapor is significantly influenced by CBL. The parameterization scheme of water vapor profiles can be expressed as 1) within the CBL (0≤ z0; 2) near the top of CBL (|z-PBL|<200), q=q₀(A-B(z-PBL)); 3) above the CBL (PBL+200≤z), q=Cq₀(z-5000-PBL), here z is height (unit is metre), PBL is the height of PBL (unit is metre). A=0.72, B=1.4×10^-3m^-1, C=?9.17×10^?5m^-1. For CBL, the IWV would be underestimated by 10% using the exponential distribution. A better estimation is achieved with this parameterization scheme proposed.