It is necessary to improve the action cross section (η × σ) of high-order multiphoton absorption (MPA) for fundamental research and practical applications. Herein, the core-shell FAPbBr/CsPbBr nanocrystals (NCs) were constructed, and fluorescence induced by up to five-photon absorption was observed. The value of η × σ reaches 8.64 × 10 cm s photon nm at 2300 nm, which is nearly an order of magnitude bigger than that of the core-only NCs. It is found that the increased dielectric constant promotes modulation of MPA effects, addressing the electronic distortion in high-order nonlinear behaviors through the local field effect. Meanwhile, the quasi-type-II band alignment suppresses the biexciton Auger recombination, ensuring the stronger MPA induced fluorescence. In addition, the core-shell structure can not only reduce the defect density but also promote the nonradiative energy transfer though the antenna-like effect. This work provides a new avenue for the exploitation of high-performance multiphoton excited nanomaterials for future photonic integration.