Due to the need for comprehensive transportation hub construction, an existing bridge in a bustling urban area with an operation duration of 25 years was required to be demolished. Based on Life Cycle Assessment (LCA), this paper proposes a scheme of “Self-propelled modular transporter (SPMT) technology + large segment cutting” to compare the carbon emissions of demolition schemes qualitatively and quantitatively. To ensure structural safety during demolition, the finite element analysis was used to simulate the entire demolishing process, and measuring points were set up to monitor the deformation of the main girder in real time under various demolition conditions. The results indicate that the scheme of SPMT has the lowest carbon emissions during the demolition stage. Additionally, the long-term prestress loss shall be considered when demolishing existing bridges; the suggested 25% proportional value for the long-term prestress loss of the Caitian Bridge is appropriate, which is determined by comparing the calculated results from various formulas. The values of the calculated and measured deformations of the main girder under different working conditions are in good agreement, with errors mostly within 10% and a maximum of no more than 14.7%. The demolition of the entire bridge was completed in a total of 28 h with little noise and pollution, and the impact on daily traffic was avoided, proving that the proposed “SPMT technology + large segment cutting” scheme is safe, efficient, and achieves the goal of green, environmentally friendly, and rapid demolition.