Tanjung Emas harbour is one of strategic harbours in Indonesia, which is located in Semarang City. Several problems arise nowadays; the drainage channel capacity decreases due to lack of treatment, rainwater storage reduced, land subsidence and the rise of tide sea level. The flood control used is polder system that classified into several clusters. The research location is focused on the Cluster IV, which the right side of harbour area. According to the data, catchment area is 29.3 hectares, the lowest elevation area is in +0,5 m, the dike elevation is +2 m LWS. Then retention pond area prepared is 900 m2 (0.3% of CA), retention pond depth - 2m LWS. Based on simulation using 2×0.3 m3/sec pump and rainfall intensity return period of 25 years 303 mm, fluctuation in water retention pond can be maintained in +0,5 m water level. It is recommended to add 0.3 m3/sec alternative pump. A pump of 3×0.3 m3/sec needs to be prepared. Based on the simulation, by Polder system, the flood problem in harbour area can be solved.