The invention relates to a cable laying construction device, in particular to a cable duct penetrating device. The space inside a cable duct is limited, and the novel cable duct penetrating traditional construction mode is low in efficiency, high in difficulty and likely to damage an old cable. According to the technical scheme, the device comprises two sets of outside pipe pulley supporting pieces, a threading pipe, at least two inside pipe pulleys, a traction rope and a cone cover; the threading pipe is formed by connecting multiple monomer sleeves, and in the working state, the two sets ofoutside pipe pulley supporting pieces are located above the two ends of the threading pipe; clamping bases at the two ends of the threading pipe are each fixedly provided with one inside pipe pulley through a support in a clamped mode; the traction rope penetrates through the threading pipe to wind around the inside pipe pulleys and the two sets of outside pipe pulley supporting pieces in sequenceto form annular connection; the cone cover is detachably installed at one end of the threading pipe. The device is simple in structure, convenient to disassemble and assemble, convenient to use and carry, and capable of enabling multiple cables to penetrate through the cable duct at a time, lowering construction difficulty and labor intensity, improving the working efficiency and avoiding the phenomenon that an old cable is damaged in the threading process.