The invention discloses a butt fusion power source control method and device for a butt fusion welding machine. The method includes the steps that set temperature determined according to a to-be-machined pipe is acquired in advance; a butt fusion power source of the butt fusion welding machine is switched on to start the butt fusion welding machine to weld the to-be-machined pipe; the actual welding temperature is detected in real time when the to-be-machined pipe is welded; and a pulse width modulation signal is generated according to the set temperature and the actual welding temperature and used for adjusting the butt fusion power source to enable the detected actual welding temperature to be close to the set temperature. The reference set temperature value is acquired in advance, and the actual welding temperature in the welding process is acquired in real time, so that the butt fusion power source supplying power to the butt fusion welding machine is adjusted in real time according to the difference between the two values, it is guaranteed that welding work can be completed within preset welding time near the reference set temperature, and it is achieved that the welding temperature and the welding time are accurately adjusted and controlled.