The D-I low temperature photoluminescence center is a well-known defect stable up to 1700 degreesC annealing in SiC, still its structure is not yet known. Combining experimental and theoretical studies, in this paper we will show that the properties of an antisite pair can reproduce the measured one-electron level position and local vibration modes of the D-I center, and are consistent with other experimental findings as well. We give theoretical values of the hyperfine constants of the antisite pair in its paramagnetic state as a means to confirm a model.