The invention discloses a marking device comprising a marking awl assembly which comprises a marking awl (11) with adjustable length, and a positioning component (2) connected with the marking awl assembly, wherein a bushing (31) and a measuring rule (32) arranged in the bushing (31) are further connected between the marking awl assembly and the positioning component (2); one of the bushing (31) and the measuring rule (32) is connected with the marking awl assembly, and the other of the bushing (31) and the measuring rule (32) is connected with the positioning component (2); the measuring rule (32) can be drawn out or retracted from the bushing (31) and fixed so as to precisely and continuously adjust the length of the marking device; and splicing tubes (4) can be spliced in different numbers according to marking lengths needed by different workpieces. The marking device can precisely and continuously adjust the length so as to be capable of marking parts with different sizes, ensuresprecise marking size, has convenient use and solves the problem of difficult marking of large workpieces because the workpieces do not need to be placed on a marking platform, thereby being capable of being used as a special tool for marking for large workpieces.