Abstract: The bearing history display technique has been proved to be an effective method in sonar signal detection. There is an interface of digital sonar between multibeam data and brightness modulation display system. This interface could result in some loss in gain obtained by the signal processor. A reasonable choice of conversion algorithm can reduce the loss to minimum. The Grey Scale Conversion (GSC) algorithm proposed in this paper is a real time digital operation. By using GSC algorithm the ability of detecting weak signal is improved when the signal to noise ratio is small, while there is almost no effect on the strong signal detection. The algorithm described in this paper is easy to implement in hardware. The computer simulation result shows a good agreement with the theoretical analysis. A brief illustration of hardware design is given.