The invention relates to a digital disc of a mechanical type digital lock, in particular to a positioning disc of a digital disc of a fixed and mechanical type digital lock. The positioning disc is an annular disc provided with a circle center hole; the outer circumference of the circle center hole is provided with a locking card slot, and the inner circumference is provided with a positioning guide sliding slot; and the inner wall surfaces of both sides of the positioning guide sliding slot along a radius direction are parallel. The positioning disc has simple structure; included angles on the circumference of 360 degrees between center lines of the locking card slot and the positioning guide sliding slot of the positioning disc of each digital disc are different from one another or not identical when the positioning disc is applied to a digital disc assembly; and the positioning disc can realize the automatic code variation of the digital lock and also form a curve locking card slot code mode through the different variation of the included angles between the center lines of the locking card slot and the positioning guide sliding slot of the positioning disc. The invention is especially suitable for being matched with the mechanical type digital locks of various safety boxes, vault doors and theftproof storeroom doors.