Based on a large number of investigation and analysis for slag detection system (SDS), a kind of automatic SDS using vibration measurements had been put forward in this paper. After studying casting process from ladle to pouring box and protection casting supporting mechanical structure, vibration dynamics model of supporting structure was established, also variation of steel water impact force and influencing factors of inspecting spot vibration are analyzed. Theories of wavelet, wavelet package and their applications in signal processing are presented. Vibration signal of steel water was processed by the way of wavelet package, then its eigenvector and tolerance range were obtained, and that can realize effective identification for steel water status. Experimental results indicate that this system is very effective and achieves anticipated outcomes.