The invention discloses a presplitting blasting system used for foundation pit excavation. The system comprises a row of blast holes formed in blasting rock, charging devices are arranged in the blastholes, electronic detonators in the charging devices are connected with an outer exploder through wires, before the main blasting area where the blasting center is located is blasted, the exploder detonates the electronic detonators in a time-difference-free manner, the charging devices are detonated, the rock is pulled cut on the excavation face, and the in-order contour line penetrating the gapis formed; each charging device comprises a sealed cylinder, a supporting rod, a bottom base layer, the corresponding electronic detonator and multiple explosives in series connection through a detonating cord, wherein the supporting rod, the bottom base layer, the corresponding electronic detonator and the multiple explosives are arranged in the cylinder, hole plugs are arranged on the top endsof the cylinders, and the cylinders are filled with water media. The system solves the problems that in traditional presplitting blasting, the mounting random of explosives is large, and the blastingprecision is not high, and the integrality of the presplitting blasting contour line is ensured.