In the work, the mutual tension of tilt grain boundaries with disorientation axes <111> and <100> in a triple junction on the example of nickel is investigated by the molecular dynamics method. The ratio of the boundary tensions found in the molecular dynamics model is compared with the ratio calculated using the Yang relation through the ratio of grain boundary energies. It is shown that both methods give close values. In addition, it was found that the elongation or contraction of low-angle tilt boundary at the triple junction motion is accompanied by the formation of zigzag displacements of atoms, which apparently appear due to the splitting and sliding of grain-boundary dislocations. The formation of new geometrically necessary dislocation during the boundary elongation occurred, as a rule, in the triple junction or in an already existing grain-boundary dislocation.