Abstract: Numerical reactor technology describes a variety of physical phenomena in the core of a nuclear reactor through highprecision, highresolution, high confidence and high fidelity numerical simulation method, based on highperformance calculation and multiphysics coupling, reveals the internal laws of various physical phenomena in nuclear reactors from mechanism, and accurately predicts the key safety parameters of nuclear reactors in service. It plays an important role in the whole life cycle of nuclear reactor R&D, design, safety analysis, operation support and decommissioning. This paper systematically introduces the main outcome of the major national science and technology project “Research on Key Technologies of CAP1400 Numerical Reactor” of “Largescale Advanced PWR and HTGR Nuclear Power Plant”. Firstly, the high fidelity reactor physics calculation codes based on deterministic method and Monte Carlo method were developed respectively, and then the pinbypin advanced subchannel analysis code and the fuel rod analysis code based on finemesh were developed. Based on those codes, the CAP1400 numerical reactor system with neutronics/thermalhydraulics/fuel performance multiphysics coupling was established. The numerical reactor system was verified and validated against the international benchmark VERA provided by CASL and AP1000 startup experimental data. For VERA problems, the comparison with the results of MC21/CTF coupling codes shows that the relative deviation of the power distribution of numerical reactor system is less than 2.5% for both Monte Carlo method and deterministic method. The maximum critical boron concentration deviation is less than 30 ppm. For AP1000 reactor of Sanmen unit 2, the deviations of developed numerical reactor compared with the measurements are as follows: 1) The maximum deviations of gray rod worth are -10.3 pcm, 7.3 pcm and 5.7 pcm, respectively; 2) The maximum relative deviation of black rod worth are 3.2%, -1.7% and 0.8%, respectively; 3) The ITC deviations are -0.597 pcm/℃, 0.280 pcm/℃, and 1.570 pcm/℃, respectively. Compared with the industry codes, numerical reactor codes have higher precision. After verification and validation, the numerical reactor codes were applied to simulate the startup experiments of CAP1400 reactor. Taking the Monte Carlo results as references, the absolute deviation of the deterministic numerical reactor code for the critical boron concentration under HZP ARO condition is -23.6 ppm. The maximum absolute deviation for the value of the gray rod group (MA to MD) is -5.2 pcm, and for the black rod group, the maximum relative deviation of the value of (M1, M2, AO, SD1 to SD6) is 2.68%. The relative deviation of the total worth of black rods is -0.08%. Assembly power distributions of 14 core conditions were compared between Monte Carlo code and deterministic code. The most positive value of relative deviation is 2.24%, the most negative value is -2.47%, the average value is -0.06% and the standard deviation is 1.02%. The above numerical results show that the developed numerical reactor analysis program has high calculation accuracy and can directly serve the design verification, startup and operation support of CAP1400.