In order to study an effect on the field uniformity of a reverberation chamber had by the mergermodes, two rectangular shell models of reverberation chamber whose volumes are approx imately equivalent are established with the saft FEKO. The dimension of No.1 reverberation chamber is 5 m×4 m×3 m. T he dimension of No.2 reverberation chamber is 4 m×4 m×4 m. T here are merger modes in the No.2 reverberation chamber. T he same mechanical stirrers are used by the two reverberat ion chambers. The electric field strength at the eight vertical points of a rectangular region in the test zone of the two reverberation cham bers is calculated separately. The standard deviation of perelectric field component and total electric field is calculated. The computed result indicates that the standard deviation of No.2 reverberation chamber is greater than that of No.1 reverberation chamber. This result indicates that the existence of the merger modes result s in the decline of the field uniformity of the reverberation chamber.