The embodiment of the invention provides a method and device for signal encoding and decoding. The method for signal encoding comprises the following steps: obtaining a frequency domain signal according to an input signal; allocating predetermined bits to the frequency domain signal according to a predetermined allocation rule; under the condition that the highest frequency of the frequency domainsignal with bit allocation is greater than a preset value, adjusting the bit allocation of the frequency domain signal; and encoding the frequency domain signal according to the bit allocation of thefrequency domain signal. During encoding, the bit allocation of a frequency domain signal is adjusted according to the highest frequency of the frequency domain signal with bit allocation, and a better encoding effect is achieved under the condition that the same number of bits are used for frequency domain encoding; during decoding, the undecoded frequency domain signal is set under the guidanceof the decoded frequency domain signal, so that the output signal achieves a better effect.