1. A three-dimensional image file searching method, comprising: storing a plurality of three-dimensional candidate image files in a database; converting each of the three-dimensional candidate image files to generate a plurality of two-dimensional candidate image files corresponding to each of the three-dimensional candidate image files; building up a plurality of second image groups corresponding to each of the three-dimensional candidate image files in the database, wherein each of the second image groups comprises the two-dimensional candidate image files corresponding to each of the three-dimensional candidate image files; receiving a three-dimensional query image file; converting the three-dimensional query image file to generate a first image group comprising a plurality of two-dimensional image files; comparing the two-dimensional image files respectively corresponding to one of the preset view angles in the first image group with the two-dimensional candidate image files in the second image groups respectively corresponding to the three-dimensional candidate image files in the database; and obtaining a search result conforming to the three-dimensional query image file, wherein the two-dimensional image files at least comprise a first two-dimensional image file and a second two-dimensional image file, and the step of comparing the two-dimensional image files respectively corresponding to one of the preset view angles in the first image group with the two-dimensional candidate image files in the second image groups respectively corresponding to the three-dimensional candidate image files in the database comprises: sequentially performing a similarity comparison procedure on the first two-dimensional image file with all the two-dimensional candidate image files of the second image groups to sieve the second image groups and to extract part of the second image groups; and then sequentially performing the similarity comparison procedure on the second two-dimensional image file with part of the two-dimensional candidate image files of the extracted part of the second image groups.