Abstract: A novel all-position welding robot for box-type steel structure was devised in order to solve the problems of low degree of automation, high risk of work high above the ground and insufficient stability of weld joint quality in the field welding for box-type steel structure. After the structural design scheme and principle of welding robot system are introduced, the welding motion process at the right-angle corner of box-type steel structure is discussed in detail according to the structural characteristics of the box-type steel structure. Then, the kinematics modeling and analysis based on Craig D-H model were carried out for its various motion states. A new method of kinematics modeling and forward solving is proposed by means of introducing one additional intermediate coordinate system under the conditions of existing connecting rod offset and joint angle variable in the process of transition movement state of welding robot. The results of working space analysis of the welding robot system show that the structural design and parameters selection are reasonable and the forward kinematics solutions is correct.