In this paper, taking gear case as research object, we studied the sound radiant efficiency of complex box-shape structure under practical stimulation by exper iment, mainly observed the difference of sound radiant efficiency between the complex structure under practice stimulation and the known simple structure. By experiment, we found that the variatioin of gear case radiant efficiency with frequency keep accordance with that of simple one as a whole, but the radiant efficiency of gear case will go beyond any calculation result of empirical formula when the frequency is below 250 Hz.Ｗe also found that stimulation changes affect radiant effieiency little by varying speed experiment, and it can be ignored in engineering calculation. The rectangle structures as gear case, possess characters of both plane and ball, and their sound radiant efficiency lie between plane an d ball region. So we propose that the mean of radiant efficiency of plane and pulse ball region can act as that of this kind of structure in practice.