Graphene has been viewed as one of the most promising materials in many fields. Recently, it has been found that by using Cu-decoration at the edge of zigzag graphene nanoribbons (ZGNR), a novel kind of planar tetracoordinate carbon (ptC) strip can be formed. In this paper, we investigate the edge-decoration of armchair graphene nanoribbons (AGNR) by various atom types and find that two new kinds of ptC strip can be effectively formed by using Be or B decoration. For the Be-decorated AGNR, the edge Be atoms take the form of a "zigzag-like" chain, and all the edge C atoms have a ptC nature. However, for the B-decorated AGNR, the edge B atoms form an infinite yet "fractured" chain consisting of separate B(4)-subunits, which results in only 50% of the edge C atoms being ptCs, in contrast with Be-decorated AGNR and Cu-decorated ZGNR. The high thermal stability of both types of ptC-based AGNR is indicated by isomeric sampling and molecular dynamics simulations.