Abstract: In contrast to the conventional pulsed active sonar, continuous active sonar is another type of sonar device that allows transmitting high duty cycle signals during the scan cycle and listening while transmitting signals, which can achieve continuous irradiation of underwater targets to eliminate the blind zone. Due to the transmission and reception mechanisms different from the pulsed active sonar, the transmission signal waveform and processing methods are also different, where the problems of the "direct wave" suppression and the compromise between TBP (time-bandwidth product) and time interval for target irradiation need taking into account. Aiming at the two problems, this paper designs a new type of pulse train signal. The signal is composed of several sinusoidal frequency modulation signal strings which are orthogonal to each other. In the post processing, three different schemes are provided for the received echo in order to achieve the optimal detection effect. The results of computer simulation show that the signal waveform and the corresponding processing method can effectively suppress the direct wave interference and give the target velocity-distance information.