Abstract: We study the direct fragmentation channel of double ionization in the collision of relativistic ions and helium dimers from a theoretical point of view. Based on the symmetry eikonal approximation, two theoretical models have been established. In one model, the two atoms of the helium dimer are regarded as a whole system, while the other model completely ignores the interaction between the two helium atoms. The numerical calculation results of the model show that the total cross-section has a strong dependence on the spatial orientation of the helium dimer. When the helium dimer is parallel to the incident ion beam, the total cross section reaches the maximum, and when it is perpendicular, the total cross section reaches the minimum. Further research found that the results of the first model is more reasonable when the helium dimer nucleus distance is small, and the second model is more accurate when the nucleus distance becomes large.