The structural, the magnetic, the transport and the half-metallic properties of quaternary Heusler alloy Fe2Co1-xCrxSi are investigated. The studies of X-ray diffraction and temperature dependence of magnetization reveal that Fe2Co1-xCrxSi alloy always maintains a high degree of order, while the Curie temperature decreases gradually with the increase of Cr concentration x. Importantly, the lattice constant and the saturation magnetic moment of Fe2Co1-xCrxSi alloy follow the Vegard law and half-metallic Slater-Pauling rule, respectively. Based on the band structure calculation, Fe2Co1-xCrxSi alloy keeps a 100% spin polarization and Fermi level moves from the top of valence band to the bottom of conduction band, depending on Cr concentration x. Our results indicate that quaternary Fe2Co1-xCrxSi Heusler alloy is a promising robust half-metallic candidate for spintronics applications.