A data reading method used in a reading device for reading a holographic storage medium is provided. The holographic storage medium has several data areas. Each data area has several data pages, and each data page forms a data image that has at least one reserved block pattern on the reading device. The reserved block pattern of the data image corresponding to a first data page is searched within a first searching region to obtain a first pattern position. The reserved block pattern of the data image corresponding to a second data page is searched within a second searching region to obtain a second pattern position. A third searching position is then determined according to the first and second pattern positions. The reserved block pattern of the data image corresponding to a third data page is searched within a third searching region whose center is at the third searching position.