1. A mood analysis method being executed by at least one processor of an electronic device, the method comprising: measuring an electrocardiogram of a user using an electrocardiograph, and detecting RR intervals in the electrocardiogram; computing low-frequency (LF) values and high-frequency (HF) values according to the RR intervals; receiving age and sex data of the user from a database, and generating standard values of sympathetic nervous system (SNS) activity and parasympathetic nervous system (PSNS) activity corresponding to the age and sex data of the user; establishing a mood display coordinate system using the standard values of the SNS activity and the PSNS activity; detecting coordinates of the LF values and the HF values in the mood display coordinate system; and analyzing a current mood of the user according to the computed coordinates, and outputting the mood of the user to a display device of the electronic device for displaying the mood for the user.