Music mood present the inherent emotional state of music on certain duration of music segment. However, the mood may vary in the music pieces. Thus it is important to investigate the duration of music segments which can best present the stable mood states in music. Four versions of music datasets with duration of clips from 4 seconds to 32 seconds are tested in this paper, and a cross test between these four version are also experimented. Better classification rates are obtained with the music segments of 8 seconds and 16 seconds. The segments with duration of 32 seconds are proved as might be not stable concerning the music mood states.