The numerical simulations of diffusion bonding of QAl10-3-1.5 pole and TC4 loop assembled structure were carried out using finite element method under the condition of 850 ℃ and 60 min，and the influence of gap on the stress field was studied. The result shows that the apparent elastic-plastic deformation of QAl10-3-1.5 pole occurs and the maximal stress emerges in joint region of QAl10-3-1.5 pole and TC4 loop. Furthermore, the diffusion stress increases with increasing the gap, and a linear relationship exists between the gap x and the diffusion stress p, which can be expressed by the function of p=118-1.46x.