The police said the crime happened in front of the couple's children.
They had been separated for two years when the stabbing occurred in February last year.
Justice Leiataualesa Darrel Clarke said domestic violence in Samoa and other communities around the world is at such a level of frequency and seriousness that deterrent sentences are generally necessary.
He said, "the prevalence, seriousness and also the silence remaining around domestic violence in Samoa was also discussed in the National Public Inquiry into Family Violence conducted by the Office of the Ombudsman".
Justice Clarke has pointed out parts of the inquiry report findings where it says family violence is affecting almost all families in Samoa.
Before the stabbing the defendant threatened to burn the mother and the children but then stabbed the woman when she tried to escape.