In April 2011, field investigation and laboratory nutrient enrichment incubation experiments were carried out to study the phytoplankton ecology and the possible nutrient limitation to the phytoplankton growth, in adjacent sea of Guanhe Estuary. A total of 68 species were identified during the investigation, of which 61 species were Bacillariophyta and the first dominant species was Skeletonema costatum. The phytoplankton cell density at each station ranged from 0.84×10⁶ to 2.25×10⁶ ind/L, with an average value of 1.54×10⁶ ind/L. The amounts of species at each station ranged from 29 to 39 and were averaged to be 35.Chlorophyll a concentrations ranged from 2.66 to 6.67 μg/L and were averaged to be 3.89μg/L, and high values were mainly found at inshore stations. The calculated Shannon-Wiener index ranged from 2.60 to 3.79 with an average value of 3.20, which showed that, during the sampling period the ecological environment in the study area was basically suitable for the phytoplankton growth. Concentrations of phosphate and nitrite measured during the investigation were in the range of 0.35 to 0.90 μmol/L and 1.57 to 3.93 μmol/L and were averaged to be 0.58 and 3.08 μmol/L, respectively, and both the two nutrients generally showed higher concentrations at inshore stations than at offshore stations. At the same time, the concentrations of ammonium, ranged from 3.14 to 5.43 μmol/L and were averaged to be 3.95μmol/L, seemed to show an opposite trend that higher concentrations were generally observed at offshore stations rather than at inshore stations. The concentrations of nitrate at each station ranged from 31.21 to 37.00 μmol/L and averaged to be at 34.55 μmol/L, and these high concentrations resulted in high N/P ratios of 42 to 112 for the study areas. Concentrations of chlorophyll a and phosphate were significantly and linearly correlated (R²=0.80), while such relationship was not observed for the two parameters of chlorophyll and DIN (nitrate+nitrite+ammonium). In the phosphate-enriched incubations, the addition of phosphate stimulated its uptake rates in the three groups, i.e., Blank, +P, and ++P with rate values of 0.36, 0.43, and 0.51d^-1, respectively. The uptake rates of nitrate and nitrite were also elevated, although not as evident as that of phosphate. During these incubations, ammonium concentrations showed an increasing trend, probably ascribed to the release of phytoplankton. The addition of phosphate also enhanced the phytoplankton growth, with the chlorophyll a peak values of 77.24, 90.57, 96.49 μg/L, respectively, for the three experimental groups at the end of incubations. During the incubation of nitrate enrichment, the addition of nitrate failed to promote its own uptake rates, with rates values of 0.39, 0.049, 0.025d^-1 for the three groups. And in these nitrate-enriched experiments, the variation curves of phosphate concentrations were similar, suggesting that the addition of nitrate also did not promote the phosphate uptakes. The concentration of nitrite increased because phytoplankton could release nitrite, and nitrite concentrations did not increase in groups of P addition might be due to the absence of N, and the released nitrite could be used for the growth of phytoplankton. The ammonium concentration was also roughly increased. The addition of nitrate did not promote phytoplankton growth, with the chlorophyll a peak value of 72.31 and 69.62 μg/L, respectively, for the groups of +N and ++N at the end of incubations, which were lower than that of the blank. These results of nutrient enrichment incubation experiments showed that the growth of phytoplankton was P-limited rather than N-limited, in adjacent sea of Guanhe Estuary in spring.