The invention discloses a method for designing a fish finder transmitter signal source, and specifically relates to a method for designing a fish finder transmitter sine wave signal source suitable for a D-class power amplifier. The method for designing the fish finder transmitter signal source adopts a Delta-Sigma modulation technology, the generated signal source only needs to connect with a D-class digital power amplifier for amplification, and after high-frequency noise is filtered through a simple low pass filter, the signal source can restore and output sine wave signals, thereby providing for a fish finder transmitter a sin wave signal source which is capable of modulating amplitude and frequency through software and is suitable for a D-class power amplifier. The requirement for bandwidth of a power amplifier tube is substantially lowered, the problem of difficult model selection of the power amplifier tube is solved, the problem that a PWM mode causes output waveform distortion due to power amplifier tube pulse loss is avoided, and the output accuracy of the signal source is substantially improved; the design of the filter is greatly simplified; and amplitude modulation and voltage regulation output of the signal source can be realized without adding of an D/A chip.