Abstract: The green tide caused by Ulva prolifera has consecutively occurred on a large scale in the Yellow Sea for 18 years, which has affected the southern sea area of Shandong Peninsula. The large amount of Ulva prolifera removed manually are needed urgerntly to be disposed harmless, economically and high efficiently, and on the other hand the nutrient levels in the shellfish culture area of Haiyang have been insufficient in recent years. To explore the potential use of natural degradation products of Ulva prolifera as the supplementary nutrients in the shellfish farming area, a floating cage is designed and made and anchored in the nearshore waters of Haiyang. For 10 consecutive days, 3 to 5 tons of fresh Ulva prolifera per day are released into the cage. The states of Ulva prolifera are monitored daily and the influences on the ecological environment are surveyed at regular intervals. The results show that at the Ulva prolifera release stations the dissolved inorganic nitrogen (DIN) increases (P＜0.05) and the dissolved inorganic phosphate (DIP) decreases (P＜0.01) in the first days of the release. After 7 days, the Ulva prolifera fragments produced during the degradation are decomposed, causing a significant increase in contents of suspended matter, dissolved organic nitrogen (DON), total nitrogen (TN) and total organic carbon (TOC) (P＜0.05). By the end of the 14-day degradation period, the pH level increases and the DIN concentration increases to 0.459 mg·L⁻¹ (P＜0.05), meeting the national fourth-class seawater quality standards. Additionally, the content of dissolved silicate (DSi) increases significantly (P＜0.05), while the contents of chemical oxygen demand (COD) and DON decrease (P＜0.05). Although the mass ratio of sulfide content in sediments increases to 3.6 times the original value (P＜0.05) at the release stations after the Ulva prolifera degradation, the sediment quality has no significant decline. The density of phytoplankton increases after the first release and the complete degradation of the algae, and the density of zooplankton remains high from the first release to the 14th day. It can be seen from these that the continuous release and degradation of Ulva prolifera in the floating cage offshore can cause the fluctuations of the ecological environment of the seawater, but the duration and scope of the influence are limited. Therefore, it can be concluded that the disposal method proposed in the study for removing Ulva prolifera has strong operability and good application prospects, particularly in the nutrient-deficient shellfish culture sea areas. However, the placement of the floating cage should be determined based on the requirements of the diffusion-type dumping zone, selecting sea areas with favorable water exchange conditions, and ensuring rational control of the release volume.