Since the end of the 20th century, giant jellyfish blooms have occurred on a nearly annual basis around the globe, with disastrous effects on the ecology of marine systems, fishery resources, coastal industries, and coastal tourism. Researchers, both domestically and abroad, have thoroughly investigated this phenomenon using nets, visual observations, underwater cameras, acoustic technology, aerial imagery, and other means to elucidate the underlying mechanisms of giant jellyfish blooms. In recent years, acoustic technology has been used to investigate the stock and behavior of giant jellyfish globally. These technologies have demonstrated favorable monitoring capabilities and the potential for their application in both resource assessment and the kinematics of the giant jellyfish. To determine the effect of Dual-Frequency Identification Sonar (DIDSON) on giant jellyfish Nemopilema nomurai monitoring in Liaodong Bay, we used DIDSON to determine quantitatively the abundance and distribution of giant jellyfish N. nomurai with individual medusae of 16–81 cm (33.01 cm±13.17 cm in July and 57.03 cm±13.44 cm in August) bell diameter in inshore waters of Liaodong Bay in July and Augus, 2017, and jellyfish anchor flow net samples were conducted simultaneously to verify DIDSON observations in the monitoring of large jellyfish. The survey results showed that DIDSON observation images can directly display the number of jellyfish and their positions in the water layer. The abundance of N. nomurai estimated by the DIDSON was 6.13 ind/(1000 m3 ), 6.71 ind/(1000 m3 ), 7.93 ind/(1000 m3 ) with mean (6.92±0.75) ind/(1000 m3 ) in July, and 1.41 ind/(1000 m3 ), 1.23 ind/(1000 m3 ), 0.55 ind/(1000 m3 ) with mean (1.07±0.37) ind/(1000 m3 ) in August. The overall average abundance of jellyfish estimated by DIDSON in July and August was 4.89 times and 3.95 times higher than that estimated by net, respectively. DIDSON images showed that N. nomurai mainly inhabited the upper and middle waters (1.1–10 m), with fewer in the bottom layer. Compared with the traditional network survey, DIDSON can more accurately observe the abundance of jellyfish in the survey area and their vertical distribution. The results suggest that it is effective to monitor the giant jellyfish using DIDSON in shallow water. The results showed that DIDSON observation can expand the monitoring content of large jellyfish, affording great advantages in the observation of its behavior. By extending the DIDSON navigation observation time and expanding its detection range, and in combination with traditional nets, the abundance of large jellyfish can be monitored more accurately.