Quantum　communication　protocols　should　take　the　effect　of　noise　into　account　in　a　real　environment.　To　analyze　the　security　of　the　quantum　B92　protocol　presented　by　Bennett　in　collective-rotation　noise　channel,　an　excellent　model　of　noise　analysis　is　proposed.　In　the　security　analysis,　the　eavesdropping　can　be　detected　with　the　increment　of　the　qubits　error　rate　(ber).　When　the　level　of　noise　less　than　0.50,　it　will　cause　a　larger　bit　error　rate　if　the　eavesdropper　Eve　wants　to　obtain　the　same　amount　of　information.　In　our　analysis,　Eve　can　maximally　get　about　50%　of　the　key　from　the　communication　when　the　noise　level　approximates　to　0.5.　We　also　presented　a　new　idea　in　analyzing　the　protocol　security　in　collective-rotation　noise　channel　with　the　idea　of　the　Markov　process.