The invention discloses a method for testing space-frequency block codes, which comprises: calculation in caussian approximation is performed to the interference distribution of received signal variable to obtain the initial probability, the typical values and the variances of sent symbols; the initial probability of the send symbols is updated, and the probability of the sent symbols is obtained; the maximum likehood ratio of the sent symbols is obtained according to the probability of the sent symbols; and the sent symbols is tested according to the maximum likehood ratio of the sent symbols. The invention also provides a space-frequency block code testing device to reduce the error floor in ultra-wideband channel, so that the system performance is improved.