With the first-principles calculations, the electronic structure and magnetic properties of KCaCX (X = O, S and Se) alloys with LiMgPdSn-type structure have been studied. The results show that KCaCO is a new bipolar ferrimagnetic semiconductor (BFS) with an integer magnetic moment of 3.00 μB at the equilibrium lattice parameter, while KCaCS and KCaCSe are fully compensated ferrimagnetic (antiferromagnetic) semiconductors (FCFS). The strong spin polarization mainly derives from the 2p electrons of C element in the KCaCX (X = O, S and Se) compounds. Under the effect of hydrostatic strain and tetragonal distortion, KCaCO alloy undergoes an interesting physics change from bipolar ferrimagnetic semiconductor (BFS) → ferrimagnetic spin-gapless semiconductor (FSGS) → general ferrimagnetic metal (GFM) transition, which indicates that the electronic and magnetic structure could be highly tuned by external temperature or pressure. A physics transition can also be found in KCaCS and KCaCSe compounds: undergoing FCFS → fully compensated ferrimagnetic semi-metal (FCFSM) → general fully compensated ferrimagnetic metal (FCFM) transitions under the hydrostatic strain and tetragonal distortion. Therefore, KCaCX (X = O, S and Se) compounds would be a series of potential candidates for new spintronics device.