A new model of high-sensitivity elliptical side-core photonic crystal-fiber sensor is designed. A circular hole and three elliptical holes of different sizes constitute the elliptical side-core photonic crystal-fiber air hole, where the e, e₁, and e₂ are the ellipticities of the elliptical holes, and the gold-nano-film is coated in the left elliptical hole with the ellipticity e. The finite element analysis software, COMSOL, is used to numerically analyze the sensing characteristics of the sensor. We found that the resonant peak of surface plasmon resonance has a high sensitivity to the change in the refractive index of the measured liquid; the sensitivity of the photonic crystal-fiber sensor varies with ellipticities e, e₁ and the gold-nano-film thickness. Within the refractive index range of 1.40-1.42, the sensor sensitivity increases with increasing e₁; within the refractive index range of 1.42-1.43, the sensor sensitivity initially decreases and then increases with increasing e₁. When ellipticity e₁ is 1.2, and the refractive index is 1.43, the sensitivity reaches as high as 31800 nm/RIU (refractive index). At a refractive index of 1.38-1.43, the sensor sensitivity increases with increasing ellipticity e. When ellipticity e is 2.3, the sensitivity reaches as high as 33200 nm/RIU. When the refractive index is 1.42-1.43, the sensor sensitivity decreases with an increase in the gold-nano-film thickness. When the refractive index is 1.43, and the gold-nano-film thickness is 40 nm, the sensor sensitivity reaches as high as 34600 nm/RIU.