To investigate the factors controlling the spring population of Acartia hongi, egg production, hatching time of egg and predation pressure were measured. Egg production was maintained the superior position between winter and spring. Egg production was positively correlated with not only water temperature when water temperature was below $7^{circ}C$ but also chlorophyll-a concentration when it was from $7^{circ}C$ to $21^{circ}C$. A regressive equation of development time$(D_e,;day)$ of eggs derived from water temperature$(T,;^{circ}C)$ was obtained as $D_e=18.9(T-0.4)^{-1.0}$, showing longer development time at water temperature below $5^{circ}C$. In Cross Correlation Analysis(CCA) to examine the time-lag relationship among abundances of developmental stages of A. hongi, egg production rate calculated by multiplying population egg production rate by hatching time showed more significant correlation with nauplii abundance than population egg production rate. Therefore, it suggests that hatching time is also recognized by a factor controlling formation of population and especially, in winter, high abundance of egg derived from high daily egg production rate and delayed hatch by low water temperature become the origin of initial spring population of nauplii. Egg predation by Noctiluca scintillans, suggesting a negative factor in formation of A. hongi spring population, was observed. During spring, A. hongi eggs were found in $2.9sim21.1%$ of individuals of N. scintillans. It was deduced that $1.2sim49.5%$ of the eggs produced by A. hongi was preyed on by N. scintillans. In conclusion, the factors controlling spring population of A. hongi were regarded as high egg production by winter generation, the delayed development time of egg by low temperature, and egg predation of N. scintillans.