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Aiming to reveal the synergistic effect of various factors on cropland evapotranspiration (ET) and net CO2 exchange (NEE) in the Huang-Huai-Hai Plain, a field experiment based on an eddy covariance technique was conducted at a typical winter wheat-summer maize field in Yucheng City, Shandong Province. Based on daily observation data of water and carbon fluxes from 2003 to 2010 and the structural equation model, the characteristics and influencing factors of ET and NEE were systematically analyzed. The results showed that the ET and NEE of different photosynthetic plants (e.g., wheat and maize) had significant differences. Seasonal variations of ET generally showed bimodal curves, with the first peak (in May) higher than the second one (in August) in each year. The ET in the wheat season fluctuated between 315.56mm and 499.54mm, with a multi-year average of 398.63mm, whereas it fluctuated from 221.68mm to 314.95mm in the maize season, with a multi-year average of 256.59mm. The significant trends of ET were found in these two different growing seasons (P<0.05). Compared with the ET, the NEE also showed a double-peak curves, with the first peak (in April) lower than the second one (in August) in each year. The NEE in the wheat season fluctuated between -367.84g/m2 and -149.93g/m2, with a multiyear average of -272.57g/m2, whereas it fluctuated from -469.63g/m2 to -118.79g/m2 in the maize season, with a multi-year average of -293.57g/m2. The net radiation was an important factor affecting seasonal changes of the ET and NEE in this field, which were mainly found to impose direct effects on the ET and NEE. As for indirect effects, radiation and temperature had great indirect effects on the ET and NEE through the leaf area index in the wheat season, whereas the indirect effect of VPD were larger in the maize season. Additionally, other environmental factors, e.g., the soil water content and wind speed had different effects on the ET and NEE in different growing seasons.