The invention discloses a horizontal drilling device which comprises a guide mechanism, a drilling mechanism, a height adjusting mechanism and a push rod. The guide mechanism comprises a horizontal guide rail pair and a vertical guide rail pair vertically supporting above the horizontal guide rail, and the lower end of a vertical guide rail body is movably connected with a seat of the horizontal guide rail; the drilling mechanism comprises an electrical motor, an electrical motor mounting plate, a small belt roller, a large belt roller, a drilling machine main shaft and a supporting seat, wherein the electrical motor mounting plate is movably connected with the vertical guide rail body, the small belt roller is fixedly connected with an output shaft of the electrical motor, one end of thedrilling machine main shaft is fixedly connected with the large belt roller, and the tip of the other end of the drilling machine main shaft is fixedly connected with a drill chuck; and the height adjusting mechanism comprises a fixing plate, a screw rod and a lock nut, wherein the lower end of the screw rod is fixedly connected with the upper end of the electrical motor mounting plate. The invention has the advantages of simple structure, convenience in operation, reliable and accurate positioning, no drilling deviation phenomenon occurred during drilling and high work efficiency.