A　general　and　efficient　method　is　presented　in　this　paper　for　studying　the　effects　of　unbalance　on　the　breathing　mechanism　of　crack.　Based　on　3D　finite　element　models　combined　with　a　nonlinear　contact　approach　for　crack　modeling,　the　method　is　free　from　the　assumption　of　weight-dominance　and　can　be　used　to　gain　deep　insights　into　the　breathing　mechanism　of　crack.　In　order　to　greatly　reduce　the　computational　time,　a　complex　free-interface　component　mode　synthesis　(CMS)　method　is　employed　to　reduce　the　order　of　the　model.　Based　on　the　proposed　method,　the　effects　of　unbalance　on　the　breathing　mechanism　of　crack　are　discussed.　Numerical　results　show　that　the　unbalance　can　lead　to　significant　changes　in　the　breathing　of　crack,　even　when　the　unbalance　force　is　about　an　order　of　magnitude　smaller　than　the　self-weight.　Moreover,　the　level　and　orientation　of　the　unbalance　have　also　remarkable　effects　on　the　breathing　behaviors　of　crack.　Besides,　a　new　universal　non-steady　breathing　phenomenon　of　crack　is　first　found　in　this　paper,　which　denotes　that　the　breathing　speed　of　a　crack　is　fluctuated　over　one　revolution　when　there　exists　residual　unbalance　in　the　cracked　rotor.