The invention discloses a position detection device and method for a steel roll system. The device comprises a total station, a reference landmark and a marker post, wherein the marker post comprisesa marker post arm, a prism, a slide block and a vacuum suction disc, the total station is bridged on one sides of the reference landmark and a to-be-measured roll shaft, the prism is fixedly connectedto the top of the marker post, the marker post arm can move up and down along the slide block and is positioned through a positioning pin, and the slide block is fixedly connected to the vacuum suction disc. The position detection device has the advantages that multiple parameter indexes of a single roll and the roll system can be simultaneously detected by virtue of the whole set of a measurement device; and by utilizing an adaptive threshold adjustment algorithm, the accuracy and fitting speed of a traditional spatial circle fitting algorithm are increased, and the device can be used for guiding the correction of the roll system, so that the productivity, quality and benefit of a product are greatly increased.