This paper presents some concepts about the kinship and introduces five possible mechanisms to resnlt in kin biased behavior, including spatial or temporal distribution, familiarity, phenotype matching, recognition alleles and green-beard effect.In rodents, kinship has very important effect on social behavior, and kin-biased behaviors occur in competition, cooperation,mating and parental care. The research on mechanisms will be benefit for understanding the origin and evolution of kin-biased behavior.