The invention provides a data hiding and encrypting method based on an optical storage medium. The method comprises the following steps: receiving an original file and converting the original file into a binary A-sequence, wherein the binary A-sequence corresponds to the pit and land of the physical run length of the optical storage medium; receiving a hiding file and converting the hiding file into a binary B-sequence, wherein binary B-sequence uses a sub-pit and sub-land coding form to make a compound code with the binary A-sequence so that at least some of the pit is filled with sub-lands in the physical run length of the optical storage medium and that at least some of the land is filled with sub-pits; the compound code is recorded on the optical storage medium to form the pit, the land, the sub-pits and the sub-lands in the physical run length.