A page aligning method for a data storage device is provided. The data storage device includes a non-volatile memory and the page aligning method includes steps of: executing a system initialization on the non-volatile memory to obtain a remaining storage capacity; selecting a number from a lookup table as an initial storage capacity according to the remaining storage capacity and a lookup table; and referring the initial storage capacity as a fixed capacity in the data storage device and writing the initial storage capacity into the non-volatile memory. A lookup table generating method and the data storage device are also provided.