Bacteriorhodopsin (BR) is the only protein in the purple membrane (PM) from Halobacterium halobium. Wild-type BR contains a single-chain polypeptide of 248 aminoacid residues and a retinal attached to Lys216 of the peptide via a schiff base, BR has the function of proton pump, Upon illumination, BR goes through a photocycle which is considered to be correlated with its proton pumping process. The good progress has been made in the studay of the structure and function of BR, but the path of photocycle and mechanism of proton pump are still not clear. The progress of the structure, photocycle and proton pump of BR in recent years are briefly introduced. And the four models of the path of photocycle which are in great argument are discussed in detail.