Spatial representation of flux data during winter wheat growing period from 2004 to 2005 was analyzed in Changwu Station, the Chinese Academy of Sciences by FSAM (Flux Source Area Model). The results indicated that flux source area (FSA, footprint) was dramatically changed during each growing stage of winter wheat under the effect level of 90% confidence. The source area of the maximum footprint was located between 7.7 m and 36.2 m from the observation point. In the prevailing wind direction, the upwind range of source area was 3.3~172.8 m, and vertical upwind range was 38.1~128.4 m.The comparison of footprint among different measurement heights showed that: with the measurement height increased up from 1.86 to 12.17 m, the length of footprint expanded from 172.8 m to 1555.2 m in the prevailing wind direction and from 123.2 m to 665.8 m in the vertical direction. The footprint fluctuated with atmospheric stability. The length of the source area is the largest under the stable atmospheric stratification with the distance of 135.3 m from the observation point, reaching 101.7 m under the condition of moderate atmospheric stratification, and the smallest is under unstable stratification with the distance of 36.3 m. Meanwhile, the source area in night is larger than that in daytime. In daily and seasonal scales, atmospheric stability has an important effect on flux source area.