Ferromagnetic-semiconductor junctions are very attractive in the science and technology of Spintronics. Among various classes of ferromagnets, half-metals are under special attention, because of their high potential for spin-injection into semiconductors. CaN crystal in metastable zinc blende structure, because of incomplete occupation of the anion p-orbital, is a half-metallic ferromagnet and thus its thin films may be proper sources for spin injection into Si semiconductor. In this research, density functional computations are used to investigate CaN/Si(001) junction and the effects of surface reconstruction on the electronic and magnetic properties of a CaN monolayer on the Si(001) surface. The most stable reconstruction pattern was argued to be c(4×2) and then a CaN monolayer are put on this surface by considering two terminations and probable configurations. The obtained results indicate nonmagnetic behavior of all investigated interface configurations. In order to study non-stoichiometric interface configurations, we added some nitrogen atoms to the stable stoichiometric configuration and relaxed again the system. It was found that the systems including 4 and 6 extra nitrogen atoms, per c(4×2) surface unit cell, may exhibit magnetic property.