Linear explosively formed penetrator (LEFP) is an optimal combination of linear cutting sword and conical shaped charge but is completely different with those two above. Initiating manner of LEFP is one of the most important factors that can affect its performance obviously. LEFP forming mechanisms of linear shaped charge initiated from the mid-point were studied with combined method of theoretical analysis, experiments and numerical simulation. Liner movement driven by the detonation wave action was analyzed as a three-dimensional issue and a synthetical model of liner movement was established. The model were verified by the penetrating experiments with the LEFP initiated from midpoint under stand-off which is 5 times distance of the LEFP caliber size. Formation processes of LEFP were described through numerical simulation and the simulation results were in concordance with those of experiments.