Abstract: Resonance calculation method is one of the key methods in the lattice code. It has a decisive impact on the calculation accuracy, geometrical and material applicability of the lattice code. At present, the resonance calculation methods used in engineering application lattice codes are mostly traditional equivalent theory method or its improved methods. This type of method has the advantages of mature theoretical model and high computational efficiency. However, due to lots of approximations, there are insurmountable shortcomings in terms of computational accuracy and applicability. The lattice codes using this type of method experience a decrease in calculation accuracy when calculating UO₂ fuel problems with ²³⁵U enrichment exceeding 5%, MOX fuel, metal fuel, and other application scenarios. The ultra-fine group resonance calculation method has the advantages of high calculation accuracy and good applicability, which can effectively overcome various disadvantages of equivalent theory method. The only drawback of ultra-fine group method is that the computational efficiency is low for the complex geometry problem because of huge number of energy groups. Therefore, it’s rarely applied in engineering application lattice codes. In recent years, a new resonance calculation theory based on Dancoff factor conservation has been proposed, such as the global-local coupling method from Xi’an Jiaotong University. The resonance calculation method combining Dancoff factor conservation theory and ultra-fine group method was researched in this paper. This method decomposed the assembly problem into multiple one-dimensional cylindrical isolated pin cell problems based on Dancoff factor conservation principle, then performed ultra-fine group resonance calculation for the one-dimensional cylindrical isolated pin cell problems to obtain the resonance self-shielded cross-sections of all resonance regions. This method retained the advantages of ultra-fine group method about high computational accuracy, strong geometric and material applicability. Meanwhile, it overcame the problem of low computational efficiency for ultra-fine group method. A new pressurized water reactor lattice resonance and transport calculation code was developed, which uses the new method introduced in this paper to treat resonance problem and uses method of characteristics to solve the neutron transport equation. A series of problems were constructed to test this new resonance calculation method. They covered the current and future potential application scenarios of pressurized water reactor. The parameters tested included the infinite multiplication factor, self-shielded cross-section of key resonance nuclides within resonance energy region, pin power distribution, and time consumption. The numerical results indicate that this method has high computational accuracy for problems with different geometries, materials and moderator densities, and has high computational efficiency when using OpenMP parallel acceleration.