The invention discloses an easily-disintegrated sandstone site expanded-base structure and an expanded-base surface protection method thereof. The easily-disintegrated sandstone site expanded-base structure comprises a straight column section and an expanded-base section. The straight column section is located in the center of the expanded-base structure and is of a straight-column-shaped structure. The expanded-base section is formed by excavating the bottom of the straight column section towards the periphery according to the designed geometrical shape. The inner surface of the expanded-base section is an expanded-base surface. The expanded-base surface is smeared with cement mortar doped with a concrete accelerator and glass fiber. An overexcavation part exceeding the designed geometrical shape of the expanded-base section is filled up with the cement mortar doped with the concrete accelerator and the glass fiber. According to the easily-disintegrated sandstone site expanded-base structure and the expanded-base surface protection method thereof, the overexcavation part is filled up and the expanded-base surface is strengthened by adopting a mode that the cement mortar doped with the concrete accelerator and the glass fiber is rapidly smeared after manual excavation so that the integrity of the geometrical shape of the expanded-base surface and the stability of the expanded-base surface can be ensured, and a scientific technology is provided for the stability of the intense weathering easily-disintegrated sandstone site manual excavation expanded-base surface.