Particle image velocimetry (PIV) technique is used to measure the flow field in the gain zone of a closed loop pulsed XeF(C-A) blue-green excimer laser. The flow velocity characteristics of the steady flow field in the center of the flow field, near the laser window and between the two parts in the discharge zone are studied. The flow field states in different time during the process of the discharge are analyzed. Furthermore, the relationships between the recovery time after discharge and the fan rotation frequency or the discharge voltage are discussed. The results show that there exit vortexes with slow flow velocity near the laser window. While in the center of the gain zone, the field is even with fast flow velocity. And in the moment after discharge, the flow field stagnation phenomenon with extremely slow velocity occurs.