Abstract: With the rapid progress of our national marine development strategy, the exhaustion of marine resources and eco-environmental problems frequently occur, which gets more and more attention on the vulnerability of the marine economy.Based on triangle model, the paper constructs the index system for vulnerability assessment of coastal urban marine economic system on pressure, sensitivity and temporariness, taking the earliest coastal open city of Yantai as the research area, the state and trend of its vulnerability of marine economic system are evaluated and analyzed.The study shows that the state of the vulnerability of marine economic system in Yantai has reduced from medium vulnerability to low vulnerability in 2004-2014.On the whole, the state of the vulnerability of marine economic system in Yantai continues reducing, and the vulnerability of the future system will be leaded by sensitivity.The change of the trend of system vulnerability from unordered development in the early to T5 (low vulnerability) in the later period and the stably and orderly decrease of the trend of system vulnerability in the middle-later period indicate that the marine economy in Yantai has been developing steadily and entering a healthy development track.