For　understanding　the　quantitative　effect　of　nonhydrostatic　stress　on　properties　of　material,　the　crystal　structure　and　Raman　spectra　of　3C-SiC　under　hydrostatic　and　nonhydrostatic　stress　were　calculated　using　a　first-principles　method.　The　results　show　that　the　lattice　constants　(a,　b,　and　c)　under　nonhydrostatic　stresses　deviate　those　under　hydrostatic　stress.　The　differences　of　the　lattice　constants　under　hydrostatic　stress　from　nonhydrostatic　stresses　with　differential　stress　were　fitted　by　linear　equation.　Nonhydrostatic　stress　has　no　effect　on　density　of　3C-SiC　at　high　pressure,　namely　the　equations　of　state　of　3C-SiC　under　hydrostatic　stress　are　same　as　those　under　nonhydrostatic　stress.　The　frequencies　and　pressure　dependences　of　LO　and　TO　modes　of　3C-SiC　Raman　spectra　under　nonhydrostatic　stress　are　just　same　as　those　under　hydrostatic　stress.　Under　nonhydrostatic　stress,　there　are　four　new　lines　with　361,　620,　740,　and　803　cm(-1)　appeared　in　the　Raman　spectra　except　for　the　LO　and　TO　lines　because　of　the　reduction　of　structure　symmetry.　However　the　frequencies　and　pressure　dependences　of　the　four　Raman　modes　remain　unchanged　under　different　nonhydrostatic　stresses.　Appearance　of　new　Raman　modes　under　nonhydrostatic　stress　and　the　linear　relationship　of　the　differences　of　lattice　constants　under　hydrostatic　and　nonhydrostatic　stresses　with　differential　stress　can　be　used　to　indicate　state　of　stress　in　high　pressure　experiments.　The　effect　of　nonhydrostatic　stress　on　materials　under　high　pressure　is　complicated　and　our　calculation　would　help　to　understanding　state　of　stress　at　high　pressure　experiments.