Abstract: As a critical step in the PWR nuclear power plant start-up process, the initial criticality test is designed to validate whether the reactor core can properly achieve the expected critical state as its numerical design. The code system NECP-Bamboo, developed independently by Xi’an Jiaotong University, was employed to verify the calculation of the initial criticality of the AP1000 reactor core. Numerical results demonstrate that the deviation of the estimated critical concentration of boron is -15 ppm, the maximum deviation of integral control rod worth is -52 pcm, the deviation of the differential boron worth is less than 0.2 pcm/ppm and the deviation of reactivity temperature coefficient is less than 1 pcm/K. The accuracy of NECP-Bamboo is similar with the high-fidelity one-step codes KENO (based on stochastic method) and VERA (based on deterministic method). The results of this work can provide further support to the nuclear safety during the start-up process of the AP1000 reactor core.