1. A music playing system, suitable for playing music based on speech emotion recognition, the music playing system comprising: a first database, storing a plurality of songs and song emotion coordinates of the songs mapping on an emotion coordinate graph; a second database, storing emotion recognition parameters; a voice receiving device, receiving a voice data; a control device, connected to the first database, the second database, and the voice receiving device, dividing the voice data into a plurality of sub voice data, analyzing frequency of the sub voice data, obtaining a current emotion coordinate of the voice data mapping on the emotion coordinate graph according to the second database, receiving settings of a target emotion coordinate, searching for at least one specific song emotion coordinate closest to a cheer-up line connecting the current emotion coordinate and the target emotion coordinate by calculating a Euclidean distance, receiving a song number information, when the song number information is N (wherein N is a positive integer), the control device determines N−2 intermediate nodes on the cheer-up line, the N−2 intermediate nodes divide the cheer-up line into N−1 equal parts, the control device determines N−2 specific song emotion coordinates respectively closest to the N−2 intermediate nodes and searches in the first database for a first song emotion coordinate closest to the current emotion coordinate and a destination song emotion coordinate closest to the target emotion coordinate by calculating the Euclidean distances between the plurality of song emotion coordinates of the songs and each of the N−2 intermediate nodes, the current emotion coordinate and the target emotion coordinate; and a playing device, connected to the control device, and sequentially playing a first song corresponding to the first song emotion coordinate, N−2 specific songs corresponding to the N−2 specific song emotion coordinates, and a destination song corresponding to the destination song emotion coordinate according to a tendency of the cheer-up line.