Abstract: Shanghai Rail Transit Line 2 is an important backbone line in the road network, of which the first phase section has been operating for almost 20 years, and there are serious hidden dangers from equipment aging and wear and tear. The upgraded line 2 signaling system adopts the new CBTC as the main signaling system for the whole line. With the existing TBTC as the solution for downgrading, the reliability and availability of the signaling system are improved. The technical scheme conforms to the development direction of the signaling system technology, meeting the long\|term operational service level needs, matching its importance in the Shanghai rail transit network. The impact on the existing operation is limited to the least and the implementation risk can be controlled.