Based on first-principles density functional calculations, we report the existence of both nontrivial band topology and superconductivity in three metallic Si allotropes, termedCmcm-Si-4, Cmmm-Si-4, and I4/mmm-Si-4. Cmcm-Si-4 and I4/mmm-Si-4 are predicted in this study, whereas Cmmm-Si-4 was proposed in previous theoretical calculations. These metastable allotropes retain their crystalline structure at ambient pressure and exhibit superconductivity at the critical temperatures of 1.2-11.4 K. We investigate the topological characteristics of the electronic states and find the weak topological nature for all three allotropes. ForCmcm-Si-4, in particular, the formation of the surface Dirac point is clearly identified. Our result provides a promising platform for realizing a topological superconducting state in all-Si systems at ambient pressure.