The structural, electronic, magnetic and optical properties of the yttrium-based binary Heusler alloy Y3Si, ternary Heusler alloy Y2CrSi and quaternary Heusler alloy ScYCrSi have been studied by first-principles calculations. The results show that the preferred configurations of Y3Si, Y2CrSi and ScYCrSi alloys are DO3 - FM, Hg2CuTi - FM and YI - FM configurations, respectively. The Y3Si alloy is a conventional metal ferromagnet. While the Y2CrSi and ScYCrSi alloys are HM ferromagnets with spin-up band gaps of 0.682 eV and 0.862 eV as well as the HM characters are maintained in the lattice constant ranges of 6.365 -7.057 angstrom and 6.029-7.129 angstrom, respectively, ensuring potential applications in spintronics. The total magnetic moments of the Y2CrSi and ScYCrSi alloys are all 2 mu(B)/f.u., satisfying the Slater-Pauling rule M-t = 18 - Z(t). Among three alloys considered, the Y2CrSi alloy has the lowest static dielectric constant, static reflective index, static refractive index, global maximum energy loss function but the highest maximum imaginary part. The phonon dispersion spectra show both Y2CrSi and ScYCrSi alloys are dynamically stable, while the Y3Si alloy is dynamically unstable. (C) 2018 Elsevier B.V. All rights reserved.