The initial phase of passive start-up of HTR-PM is directly simulated to estimate the variations of fission rate and power with time, and the dynamic control rod lifting process of passive start-up is simulated using the MC program RMC. During the passive initiation phase of the reactor, the axial neutron flux distribution within the core has been subjected to a rigorous statistical characterization. The empirical analysis delineates that the neutron flux profile within the hybrid core architecture exhibits a parabolic trajectory, ascending to a maximum before subsequently diminishing with increasing elevation. Notably, the neutron flux intensity at the basal region of the hybrid spherical bed markedly surpasses that at the zenithal extremity. Additionally, the temporal evolution of neutron flux distribution reveals remarkable invariance across sequential temporal increments, underscoring a consistent phenomenological pattern throughout the transient analysis window.