Basic principle and equipment parameters of marking machine are introduced. The marking machine used in Masteel big bloom continuous casting machine is for round billet section of spraying number and character. Equipment are analyzed in detail and all kinds of problems in use process are put forward, for example, the character lost, fuzzy characters and blocking problems. The causes of these problems are analyzed. After the exploration and improvement, the material of spray wire is improved, and wire feeding unitand testing device are optimized. The problem of instability of the machine in use is solved completely, which can meet the production requirement for spraying casting number, and the labor intensity of the workers is reduced.