Recent researches have shown bilingualism has an influence on cognition,both negative and positive.This essay aims to discuss the cognitive disadvantages and advantages bilingualism brings,by emphasizing how it affect children’s cognitive devel opment.It will first briefly introduce the disadvantages such as a lower verbal fluency and vocabulary deficit,and then analyse the advantages on non-verbal cognition and attention controlling,a more sensitive metalinguistic awareness and a lower decline rate of cognitive processing.