The waterproofing quality of immersed tunnel segment has a significant influence on tunnel operation safety and tunnel service life. The enclosed waterproofing technology of “waterproofing base steel plate + spraying polymer cement on roof and sidewall” is adopted in Honggu Immersed Tunnel in Nanchang. The technologies include: 1) Use steel plate of 6 mm with anchor to reduce adsorption force. 2) Polymer cement spraying on roof and sidewall. The enclosed waterproofing technologies are improved by staggered joints welding of base steel, changing the connection mode of anchor bar, reinforcing of weak points and strengthening test and monitoring.