The invention relates to a liquid prism refractometer, in particular to a novel structure of the liquid prism refractometer used for measuring liquid refractive index and a work principle thereof, belonging to the technical field of devices for measuring the refractive index, concentration and density of liquid. The refractometer comprises a monochromatic light source (1), a hollow triple prism (5) and an optical receiving device (6), wherein the hollow triple prism (5) is made of transparent material without limitation of the refractive index, the outer side of a light incidence surface (2) is ground to be a rough surface, and an included angle between the light incidence surface (2) and a light-emitting surface (3) is 60 degrees; an upper bottom surface (4) is provided with a movable cover which is used for canning and pouring the liquid; and a liquid prism can be formed when the liquid is filled. Therefore, the refractive index, the concentration value and the density value of the liquid to be measured can be measured by utilizing the measurement principle of a glancing incidence method. Compared with the existing common prism measuring instruments such as Abbe refractometer and the like, the liquid prism refractometer has wider refractive index measuring range, and simple structure, easy manufacturing, lower cost and higher accuracy.