The invention relates to the technical field of data hiding, in particular to a data hiding method and a data hiding system. An image is used as a data carrier; after secret data is converted into a bit sequence by a sending end, the values of each bit in the bit sequence are hidden in the image; the image hidden with the secret data is obtained and is sent to a receiving end; and the receiving end can extract the hidden secret data from the image according to a corresponding secret key. During data hiding, each square image block can hide two-bit data through inverse number odd-even properties of a pixel gray value sequence of two diagonal lines of each square image block, so that the volume of data hidden in the image is twice of the number of the image blocks split by the image.