Abstract: The influence factors such as the content of diffusible hydrogen in weld metal,the hygroscopicity in electrode coating and the toughness of weld metal of basic electrode are studied and discussed.The authors developed for coal mine hydraulic stand a special electrode LZ55 with high toughness,high anti-cracking property and ultralow diffusible hydrogen in weld metal.It has been proved to have exellent adaptability in welding the hydraulic stands of low alloy steel of 400~450 N grade yield strength.The electrode has been used satisfactorily in the production of hydraulic stands FDT4×550,with all properties up to industrial standards.