Depth detection tool for subsea tree gland step, and method thereof

The invention discloses a depth detection tool for a subsea tree gland step, and a method thereof. The detection tool is placed on the subsea tree gland step and comprises a measurement head, a sliding needle, a datum plate, a lever and a dial indicator, wherein the measurement head is in contact with the lower surface of the subsea tree gland step when the detection tool carries out measurement;the sliding needle is connected with the measurement head and is driven by the measurement head to upwards move; the datum plate is arranged on the upper surface of the subsea tree gland step when thedetection tool carries out measurement; the lever is arranged above the sliding needle, and the sliding needle upwards moves until the sliding needle supports the lower part of the lever; when the lower part of the lever is supported by the sliding needle, a rotating spindle is in contact with the lever to drive the lever to rotate; and a measurement rod arranged on the dial indicator is in direct contact with one side of