Two new monoclinic silicon allotropes P2/m Si54 and V-Silicon are proposed. Mechanical, thermal and dynamic stability of P2/m Si54 and V-Silicon were verified by elastic constants, (AIMD) simulations and phonon spectra. The enthalpy of V-Silicon exceeds that of diamond Si by only 0.04 eV/atom, which indicates that it has excellent stability. V-Silicon has an indirect band gap with a band gap of 1.00 eV, P2/m Si54 has a quasi-direct band gap with a band gap of 0.60 eV. Additionally, P2/m Si54 and V-Silicon show excellent light absorption performance in different wavelength ranges in the visible region.