Penetration control is an important development direction in the field of welding process control.Its key difficulty is to obtain the characteristic information of weld penetration state which is used to describe the penetration state of the weld.According to the problems of low robustness and poor real-time performance of traditional penetration detection methods,a laser photoelectric conversion method is proposed.This method can realize the real-time extraction of the oscillation frequency of the GTAW molten pool.Using the change feature of o scillation frequency of the molten pool from incomplete penetration to full penetration,a penetration control algorithm under step welding conditions is designed,and penetration control experiments are carried out on the workpieces with different heat emission conditions and different amount of weld offset.The results show that the measurement method can realize the real-time sensing of the oscillation frequency of the molten pool during the welding process,and the control algorithm has strong robustness to factors such as heat emission conditions and the amount of weld offset,and the control effect is good.The front and back sides have uniform melting width and good continuity.