The optimal design problem of the bimodal transit network (i.e., the sparse express lines and the dense local lines) fed by shared bikes has not been well studied. In light of this, this study presents a continuum model to jointly optimize the bimodal transit system and shared bikes simultaneously in a grid network. A series of numerical cases are examined for comparing with the scenario of such system only accessing on foot. The results indicate that the generalized cost saving ranges from 12% to 60%. Meanwhile, transit operator costs are decreased due to an optimized service headway and line/stop spacing.