Abstract: The baseline upgrading situation of Shenzhen Metro Line 5 signaling system is introduced. The upgrading and optimization features of automatic train control (ATC) sub\|system, computer\|based interlocking (CBI) sub\|system, automatic train supervision (ATS) sub\|system, maintenance support system (MSS) sub\|system and data communication system (DCS) sub\|system are expounded. By referring to the baseline upgrading experience of Shenzhen Metro Line 5 signaling system, the commonly encountered situation and corresponding treatment measures during baseline upgrading are summarized.