An accurately positionable computer host power-on detection machine comprises a detection box with an opening on the left side, the detection box is internally connected with a detection discharge block through a lifting device, the right part of the detection discharge block is provided with a positioning interception block, the height of the positioning intercept block is the same as the host and the center of the positioning interception block is provided with a detection port of 0.6-0.8 times the size of the rear side plate of the host, the inner side of the upper plate of the detection box is connected with an upper limit plate through a connecting plate, the detection box is provided with a positioning and clamping device cooperated with the left and right side plates of the host, and the inner side of the right side plate of the detection box is provided with a detection device which enables a detection insert block to move horizontally left and right.