The mixing of two phases and the influence of drop size on mass transfer were studied in a spray column with pneumatic nozzle. A mass transfer model including the effects of backmixing and drop size distribution ot the dispersed phase was established. The equations of the model were solved by the steady-state concentration profile method. The backmixing numbers (Peclet Numbers) of two phases and the true mass transfer coefficients of the drops were obtained. The equations can be used to calculate the concentration profile in a spray column with pneumatic nozzles of different structure and size.