After studying on the forms, hatching, production rhythm of eggs and eggs in the sea-bottom muds produced by Acartia spinicauda and A. pacifica living in Xiamen waters, the seasonal succession model of these two Acartia species in Xiamen waters is suggested: A. pacifica is dominant in the winter and spring. In the late spring and early summer it produces diapause eggs which sink into sea bottom and bury in the muds and hatch continually to recruit its population. This is why it appears yearround in Xiamen waters, but its population quantity is decreased in summer and autumn. The population quantity is resumed in the next winter since the diapause egg production is ceased. A. spinicauda occurs only in summer and autumn. Because it produces one kind of egg in the late autumn and early winter which could not hatch properly, it is soon replaced by A. pacifica.