Concerning the blast-resistant analyses and design of protective structures under potential far-range large-yield chemical explosions and the industrial gas/fuel explosions, the dynamic behaviors of RC slab under long-duration near-planar blast loadings are studied both experimentally and numerically. Firstly, unlike the conventional short-duration explosion with spherical waves, aiming to generate the long-duration near-planar blast loadings on the structural members, a specified apparatus including a confined shot cavity, a cubic-like steel frame and the plane charge explosion technique (PCET) is developed. Secondly, the field explosion test on five one-way simply-supported RC slabs with the dimensions of 2400×1000×100 mm3 is conducted, in which the magnitudes and durations of the near-planar blast loadings are varied within 0.1–0.4 MPa and 85–135 ms, respectively. Then, by adopting the Structured-Arbitrary-Lagrange-Eulerian (SALE) solver and Fluid-Structure Interaction (FSI) algorithm implemented in the commercial finite element program LS-DYNA, the above field test is simulated numerically. By comparing with the test data including the overpressure-, rebar strain- and displacement-time histories as well as structural post-blast damage, the validity of the adopted finite element analysis (FEA) approach for the long-duration explosion scenarios with multi-point detonations is verified comprehensively, and the propagation of blast waves, dynamic responses and damage patterns of RC slab are assessed. Finally, the applicability of single degree of freedom (SDOF) approach recommended in the specification UFC 3–340–02 to predict the maximal mid-span deflections is further verified. The present work can provide helpful references for the long-duration explosion loadings test technique and the blast-resistant design of protective structures.