Abstract: To investigate the fragment impact initiation characteristics of JOL, a typical HMX-based insensitive pressed explosive, one-dimensional Lagrangian experiments under chemical explosion loading were designed and conducted. Based on the SURF reaction rate model, parameters for the shock initiation reactive flow model were calibrated. Numerical simulations of fragment impact under various working conditions were performed to study the influence laws of fragment characteristics on the shock initiation of JOL explosive. The results show that the calculated distances to detonation and pressure histories at different Lagrangian positions for JOL agree well with experimental data, validating the accuracy of the calibrated SURF reaction rate model parameters. As loading pressure increases, the detonation growth rate within the explosive accelerates; simultaneously, as hot-spot chemical reactions accumulate behind the wave front, both propagation velocity of the wave front and explosive reaction rate further increase. The SURF reaction rate model captures the shock desensitization caused by detonation wave diffraction, characterized by a shrinking dead zone during propagation. Additionally, the critical initiation velocity decreases with larger fragment diameters or thinner shell thicknesses. These findings provide theoretical and technical support for the safety assessment of ammunition under fragment impact.