Three different convergent nozzles(axis symmetrical, rectangular, and S -curved)with the same inlet, outlet areas and lengths, the radiation characteristics in different detecting planes of which were experimentally investigated. The results show that in the horizontal plane, the thermal radiation intensity of three nozzles all decreased with the increase of detecting angle, the S-curved nozzle has the best infrared suppressing characteristics; in the vertical plane, the S-curved nozzle also has the best infrared suppressing characteristics. While being detected from upwards, the intensity of S-curved nozzle increased first then decreased with the increase of angle, and the largest radiation magnitude appeared in the detecting angle 10°. Compared with the axis nozzle, the thermal radiation intensity of rectangular and S-curved nozzles decreased in turn. In the direction of right behind the nozzles, the thermal radiation of rectangular and S-curved nozzles decreased by 33.2% and 80.2% separately, compared with the axis nozzle.