The invention discloses an illumination system for automatically adjusting an illumination direction according to a human body signal, which comprises an illumination component, a human body signal detecting unit, a processing unit, an illumination direction adjusting unit and a memory unit. The illumination component projects an illumination light beam along the illumination direction; the human body signal detecting unit detects at least one human body signal emitted by a user, and produces an intensity signal by the human body signal; the processing unit receives the intensity signal so as to send out an illumination direction adjusting signal; and the illumination direction adjusting unit adjusts the illumination direction according to the illumination direction adjusting signal. The memory unit is electrically connected to the processing unit. The processing unit also includes one illumination direction operational program which is supplied to the processing unit to calculate one angle coordinate to be adjusted due to the illumination direction according to the intensity signal.