A horizontal five-axis turning plate type machining center, comprising a support base, a bed arranged on the support base and a column arranged on the support base, wherein the bed and the column are fixedly connected through a connecting arm, the support base is provided with a turning plate device which comprises a turning plate having a lower part hinged to the support base and a first driving unit capable of driving the turning plate to turn over, and an X-direction sliding plate capable of sliding in an X direction on the bed and a second driving unit capable of driving the X-direction sliding plate to slide are arranged on a side, facing the column, of the bed; and a third driving unit capable of driving a workbench to perform position conversion between the turning plate and the X-direction sliding plate is arranged on the turning plate, the X-direction sliding plate is provided with a locking mechanism capable of locking the workbench, the column is provided with a Y-direction sliding plate, the Y-direction sliding plate is provided with a Z-direction ram, and the Z-direction ram is provided with a milling head, wherein the locking mechanism comprises a T-shaped block, a supporting block, a pull rod, a disc spring, a spring and a fourth driving device for driving the pull rod to move axially, the supporting block is fixed on the X-direction sliding plate, the pull rod passes through the T-shaped block and the supporting block, and an end of the pull rod is provided with a first radial protrusion capable of pulling the T-shaped block; the spring is arranged between the T-shaped block and the supporting block, the pull rod is sleeved with the disc spring, and the disc spring and the T-shaped block are respectively positioned on an outer side and an inner side of the supporting block; and the pull rod is provided with a second radial protrusion which limits the disc spring on the pull rod, two ends of the disc spring abut against the supporting block and the second radial protrusion respectively, and the back of the workbench is provided with a T-shaped locking groove matched with the T-shaped block, and wherein the Y-direction sliding plate is arranged on one side of the column, and a tool changer is arranged on another side of the column; a side surface of the column is provided with a first Y-direction lead screw, a second Y-direction lead screw, and a first Y-direction driving motor and a second Y-direction driving motor which drive the first Y-direction lead screw and the second Y-direction lead screw respectively; and the Y-direction sliding plate is mounted on the first Y-direction lead screw and the second Y-direction lead screw, two Z-direction sliding rails are arranged on the Y-direction sliding plate, two sides of the Z-direction ram are mounted on the Z-direction sliding rails through Z-direction sliding blocks, and the milling head is an A/B angle milling head. wherein the locking mechanism comprises a T-shaped block, a supporting block, a pull rod, a disc spring, a spring and a fourth driving device for driving the pull rod to move axially, the supporting block is fixed on the X-direction sliding plate, the pull rod passes through the T-shaped block and the supporting block, and an end of the pull rod is provided with a first radial protrusion capable of pulling the T-shaped block; the spring is arranged between the T-shaped block and the supporting block, the pull rod is sleeved with the disc spring, and the disc spring and the T-shaped block are respectively positioned on an outer side and an inner side of the supporting block; and the pull rod is provided with a second radial protrusion which limits the disc spring on the pull rod, two ends of the disc spring abut against the supporting block and the second radial protrusion respectively, and the back of the workbench is provided with a T-shaped locking groove matched with the T-shaped block, and wherein the Y-direction sliding plate is arranged on one side of the column, and a tool changer is arranged on another side of the column; a side surface of the column is provided with a first Y-direction lead screw, a second Y-direction lead screw, and a first Y-direction driving motor and a second Y-direction driving motor which drive the first Y-direction lead screw and the second Y-direction lead screw respectively; and the Y-direction sliding plate is mounted on the first Y-direction lead screw and the second Y-direction lead screw, two Z-direction sliding rails are arranged on the Y-direction sliding plate, two sides of the Z-direction ram are mounted on the Z-direction sliding rails through Z-direction sliding blocks, and the milling head is an A/B angle milling head.