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The search for candidates of spintronic materials, especially among the two-dimensional (2D) materials, has attracted tremendous attentions over the past decades. By using a particle swarm optimization structure searching method combined with density functional calculations, two kinds of boron carbonitride monolayer structures (B _4 CN _3 and B _3 CN _4 ) are proposed and confirmed to be dynamically and kinetically stable. Intriguingly, we demonstrate that the magnetic ground states of the two B _x C _y N _z systems are ferromagnetic ordering with a high Curie temperature of respectively 337 K for B _4 CN _3 and 309 K for B _3 CN _4 . Furthermore, based on their respective band structures, the B _4 CN _3 is found to be a bipolar magnetic semiconductor (BMS), while the B _3 CN _4 is identified to be a type of spin gapless semiconductor (SGS), both of which are potential spintronic materials. In particular, carrier doping in the B _4 CN _3 can induce a transition from BMS to half-metal, and its spin polarization direction is switchable depending on the doped carrier type. The BMS property of B _4 CN _3 is very robust under an external strain or even a strong electric field. By contrast, as a SGS, the electronic structure of B _3 CN _4 is relatively sensitive to external influences. Our findings successfully disclose two promising materials toward 2D metal-free spintronic applications.