1. A signal classifying method, comprising: obtaining a spectrum fluctuation parameter of a current signal frame; buffering the spectrum fluctuation parameter of the current signal frame in a first buffer array if the current signal frame is a foreground frame; if the current signal frame falls within a first number of initial signal frames, setting a spectrum fluctuation variance of the current signal frame to a specific value and buffering the spectrum fluctuation variance of the current signal frame in a second buffer array; otherwise, obtaining the spectrum fluctuation variance of the current signal frame according to spectrum fluctuation parameters of all signal frames buffered in the first buffer array and buffering the spectrum fluctuation variance of the current signal frame in the second buffer array; and calculating a ratio of signal frames whose spectrum fluctuation variance is above or equal to a first threshold to all signal frames buffered in the second buffer array, and determining the current signal frame as a speech frame if the ratio is above or equal to a second threshold or determining the current signal frame as a music frame if the ratio is below the second threshold.