The invention discloses a method for monitoring the 
electric arc length through 
electric arc voltage signals. According to the method for monitoring the 
electric arc length through the electric 
arc voltage signals, by means of real-time detection of electric 
arc voltage signal waveforms in the process of 
welding or additive manufacturing of an electric arc, an electric 
arc voltage time-domain 
signal waveform higher than an electric arc 
voltage threshold value is extracted, so as to obtain an electric arc 
voltage time-domain feature waveform, 
noise elimination is conducted on the electric arc voltage time-domain feature waveform through 
wavelet analysis, low-frequency components of the electric arc voltage time-domain feature waveform are extracted through 
wavelet packet analysis, an electric arc voltage 
signal low-frequency component feature waveform graph is drawn, the electric arc voltage signal low-frequency component feature waveform is substituted into an electric 
arc length mathematical model, an electric 
arc length change time-domain waveform in the 
machining process is obtained through calculation, and the electric 
arc length at any 
machining moment in the 
machining process can be obtained through the electric arc 
length change time-domain waveform. By the adoption of the method for monitoring the electric arc length through the electric arc voltage signals, offline detection and online monitoring of the electric arc length in the electric 
arc welding processes of TIG, MIG, MAG, PAW and the like and in the 
metal material electric arc additive manufacturing process can be achieved.