Elemental boron has evoked substantial interestbecause of its chemical complexity in nature. It can form multicenter bonds due to its electron deficiency, which induces the formation of various stable and metastable allotropes. The search of allotropes is attractive for finding functional materials with fascinating properties. Using first-principles calculations with evolutionary structure searches, we have explored boron-rich K–B binary compounds under pressure. A series of dynamically stable structures (Pmm2 KB5, Pmma KB7, Immm KB9 and Pmmm KB10) containing boron framework with open channels are predicted, which can be possibly synthesized under high pressure and high temperature conditions. After removal of K atoms, we obtain four novel boron allotropes as o-B14, o-B15, o-B36 and o-B10, which exhibit dynamical, thermal and mechanical stability at ambient pressure. Among them, o-B14 contains unusual B7 pentagonal bipyramid and appears bonding combination seven-center-two-electron (7c–2e) B–B π bonds, which is first time to be identified in three-dimensional boron allotropes. Strikingly, our calculation reveals that o-B14 exhibits as superconductor with a Tc value of 29.1 K under ambient conditions.