The invention provides a liquid crystal composition and its liquid-crystal display device. The liquid crystal composition comprises at least one compound as shown in the general formula I-1 and/or I-2; at least one compound as shown in the general formula II; at least one compound as shown in the general formula III; at least one compound as shown in the general formula IV; and at least one compound as shown in the general formula V. The liquid crystal composition has characteristics of wide nematic-phase temperature range, high dielectric anisotropy, high optical anisotropy, high clearing point, low viscosity, low threshold voltage and the like. The liquid crystal composition is suitable for a liquid-crystal display element. By the use of the liquid crystal composition, the liquid-crystal display element has characteristics of low threshold voltage, fast response speed, excellent power-saving property and the like.