Abstract: A time-domain analytical Green's function was proposed for air which is characterized by quadratic attenuation. Based on the function and Rayleigh's integral, a time-domain model was created to compute transient acoustic field radiated from circular piston into air. The simulation shows that compared with non-attenuation case, in air, high frequency component is greatly weakened, an evident drop as a function of wave propagation distance is found in signal amplitude, and a decrease is observed in near-field length. The study provides a fast computing approach for the air-coupled acoustic field simulation. At the same time, it presents a good reference for air-coupled transducer design and calibration.