The invention discloses a retaining and protecting method for a vacuum preloading foundation excavation at a soft soil road section, which is used for vacuum preloading for the soft soil road section when in the retaining and protecting for the foundation excavation in the underpass construction of the soft soil road section. In the method, firstly, cement mixing piles are piled at the corresponding positions of the ground level road at the two sides of an underpass section and are used for enclosing and dividing the soft soil road section into a plurality of closed regions, plastic drainage boards are piled in each closed region at a certain interval, a sand cushion is laid at the ground of the closed region and is internally embedded with a strainer, and the sand cushion is covered by a sealing film to be isolated from atmosphere; then, a vacuum pump is communicated with the strainers in the sand cushion and exhausts the air in the sealing film; finally, the vacuum degree in the sealing film can be kept to be more than 80KPa; the degree of consolidation of the foundation is more than 80% when stopping the preloading for the underpass section, then the foundation excavation is excavated by the underpass section, and a retaining wall of the underpass section is arranged.