Abstract: On basis of the similitude principles,the conception of virtual simulative component and the auxiliary value of welding residual stress are deduced by the welding conduction theory,and the relation of the welding residual stress between the simulative component and the practical component is attained. Moreover,the welding experiment about the simulative plane and the practical plane proves the correctness of the relation,which the proportionality coefficient of dimensions between the simulative plane and practical plane is 1:1.5. This provides a new idea to predict the welding stress distribution of large practical structure by the contractible physical model and has owns important theory meaning and practical engineering significance.