Abstract: Abstract: The rapid development of modern agriculture in China has put forward higher requirements for agricultural machinery operation. In order to meet the requirement of agricultural machinery scale management and market service, operation area should be measured by using a kind of accurate, real-time and convenient method. The GNSS (global navigation satellite system) receiver installed in agricultural machinery can provide operation trajectory data in real time. The paper reports a vector buffer algorithm and a raster buffer algorithm for operation area measurement based on GNSS trajectories of agricultural machinery. The vector buffer algorithm calculates the area of operation buffer polygon which is generated by intersecting and merging the part line buffers based on trajectory segments using data analysis method of the GIS (geographic information system). The raster buffer algorithm calculates the area of entire operation buffer which is covered by a certain number of unit grids with known area value. At present operation area is measured by using the conventional distance algorithm based on the product of swath width and distance of trajectory segments. The tests of full-width operations and overlap operations were carried out to compare area measurement accuracy of these two buffer algorithms with the distance algorithm in three different GNSS positioning accuracies of RTK (real time kinematic), decimeter-level and single-point. Full-width operation was implemented in the control of automatic navigation system for agricultural machinery. Overlap operation was achieved by setting up different overlapping rates of 5%, 10%, 15%, 20% and 25%. The results showed that in the full-width operation tests the distance algorithm had higher area measurement precision in any GNSS positioning accuracy, and the mean of relative error was 0.72%. Compared with the distance algorithm, the two buffer algorithms precisely measured operation area only in differential GNSS positioning accuracy. Using RTK GNSS positioning, the relative errors of the vector buffer algorithm and the raster buffer algorithm were 0.31% and 0.18%, respectively. Using decimeter-level GNSS positioning, the relative errors of the two buffer algorithms were 2.43% and 1.44%, respectively. However, in overlap operation tests the relative error of the distance algorithm increased significantly with the increasing of overlapping rate in any GNSS positioning accuracy. Area measurement precisions of the buffer algorithms were not affected by the overlaps. The relative errors of the vector buffer algorithm in GNSS positioning accuracies of RTK, decimeter-level and single-point were 0.48%, 3.13% and 5.52%, respectively. The relative errors of the raster buffer algorithm in GNSS positioning accuracies of RTK, decimeter-level and single-point were 0.11%, 2.77% and 5.33%, respectively. In China it cannot avoid the operation overlaps while agricultural machineries are controlled by drivers, and therefore the buffer algorithm can provide more accurate and convenient method for operation area measurement.