The fusion neutronics simulation has been a great challenge to the numerical calculation of the neutron-transport equation. The key is how to deal with the features of fusion devices, such as large-scale, complex geometric models, large vacuum regions, etc. NECP-FISH, a code developed by Nuclear Engineering Computational Physics (NECP) laboratory of Xi'an Jiaotong University, is used to address this challenge. NECP-FISH adopts a deterministic numerical method instead of the Monte Carlo method because the deterministic numerical method is of higher computational efficiency and costs less computational time. To deal with large vacuum region, large-scale and complex geometric model, the first order neutron-transport equation is solved, the spherical harmonics function and the finite element method are applied to the expansion of angle and space. NECP-FISH has been validated by benchmark problems such as strong absorption problem, internal void problem, and Kobayashi series of problems. What’s more, NECP-FISH builds the user interface based on the platform SALOME so that users can visually build the necessary models for problems. NECP-FISH has been applied to the neutronics calculation of the breeder unit of Helium Cooling Ceramic Breeder (HCCB) and the blanket of CFETR. The numerical results demonstrate that the NECP-FISH code can efficiently solve the neutron transport problem of the fusion reactor.