The invention provides an InP quantum dot and a preparation method thereof. The preparation method includes the steps that 1, a first InP core and an InP nanocluster are adopted to prepare a second InP core; 2, with the second InP core as the core, a Zn precursor, a Se precursor and an optional S precursor are made to form a shell containing ZnSexS1-x or ZnSe / ZnS on the surface of the second InP core with an epitaxial growth method, and the InP / ZnSexS1-x quantum dot or the InP / ZnSe / ZnS quantum dot is obtained, wherein 0<x<=1. By adopting the first InP core and the InP nanocluster to prepare the second InP core, the obtained second InP core is more uniform in particle size, and the peak width at half height is reduced; the shell of the obtained InP quantum dot contains both Se and S, so that the coating thickness of the shell is further increased, and the luminous efficiency and stability of the InP quantum dot are further improved.