Calanus sinicus is an ecologically important copepod species found in the shelf waters of the western part of the North Pacific Ocean. Over-summering strategies are important for the population dynamics of C. sinicus. In this paper, we studied the lipid content as well as the abundance and structure of the C. sinicus population in the southern Yellow Sea and East China Sea in summer to enhance our understating of the various over-summering strategies. In August 2011, C. sinicus was collected using a 500 μm mesh ring net (mouth opening, 0.5 m²). The samples used for studying the abundance and structure of the population were preserved in 5% formalin seawater solutions. The total lipid content was extracted from fifth copepodite (C5) or female C. sinicus with 3 mL chloroform: methanol (2 ∶ 1 v/v) at -20℃ for 16 h and weighted on a Cahn electrobalance (±100 μg). The lipid content was separated using a chromatographic method and analyzed in duplicate using Iatroscan MKS-6 with flame ionization detector (FID). The results showed that certain regions in the Yellow Sea Cold Bottom Waters (YSCBW, water temperature < 10℃) had the highest amount of C. sinicus ranging from 93.3 ind/m³ to 446.9 ind/m³ (mean, 242.6 ind/m³). The area near the shore of the East China Sea also showed an abundant C. sinicus population (range, 60.8-148.4 ind/m³; mean, 91.0 ind/m³). In addition, regional differences were observed with regard to the structure of the population. In the southern Yellow Sea, C5 accounted for 77.4% of the total population in the YSCBW, while C5 and females contributed to 32.3% and 51.8%, respectively, out of the YSCBW. In the East China Sea, the structure of the population was similar to that outside the YSCBW with 33.2% of C5 and 41.3% females. The results of the abundance and structure of the population indicate that the area near the shore of the East China Sea may also act as a preservation area for C. sinicus in summer along with the YSCBW. The total lipid content in female C. sinicus was approximately 5.4-17.2% of their dry body mass, while C5 had higher lipid content (22.4%-40.1%). The lipid content of C5 in the YSCBW was 43.1 μg/ind, while the lipid content of the females in the YSCBW (mean, 24.6 μg/ind) and at the area near the shore of the East China Sea (mean, 18.2 μg/ind) was lower than C5 in YSCBW. The major lipid classes were wax ester and phospholipid and together they comprise of approximately 90% to the total lipid content. The C5 in the YSCBW can survive longer (18 days) than C.sinicus in other areas (≤6 days) by utilizing the lipid content as their sole energy source for their basic metabolic needs. However, this is still insufficient for successful over-summering of C.sinicus. The C5 in the YSCBW can use stored lipid and sustain on a limited food supply during over-summering, while C. sinicus in other areas require active feeding to survive during the summer.