Abstarct: Control of the manual gas mextal arc welding process with novel view in application of sliding mode control in industrial processes to increase the quality of the weld and the facility of the welder task is presented in this thesis. The quality of the weld is extensively affected according to the uncertainties in the process, where the most of them is the vibration of the welder hand. Therefore, robust control is applied to overcome these uncertainties. The gas mextal arc welding model is introduced and investigated for specifying the bound of uncertainties. To control the arc length, sliding mode controller is designed and simulated baxsed on this model. Measurement of welding current and arc length has been noticed in the control system and the PWM inverter baxsed power supply is used in welding machine to provide voltage. The novelty of this thesis is on the application of sliding mode theory in order to suppress the uncertainties in industrial gas mextal arc welding system and the steps of design and simulation has been performed. It tried to have an appropriate control on the process by considering , to some extend, practical conditions in a manual welding, especially the presence of welding power supply dynamics in simulations. In this way, fuzzy sliding mode control approach is also proposed for enhancement of arc length control.