In the measurement of source emissions， it is inevitably interfered by the gas emissions from the adjacent fields and turbulence， which affects the accuracy of gas detection. In order to improve the measurement accuracy， the measurement method of composite non-point sources non-uniformity methane emissions based on laser spectrum detection has been studied. Moreover， the interference in external environment is reduced with multiple self-calibration measurements. A detection system for composite non-point source emissions has been established， and the detection method of eliminating gas fluctuation has been proposed. First， the accuracy verification test has been carried out. The standard deviation of source a is 0.17， and that of source b is 0.18. Subsequently， a comparative test has been carried out with the extraction method of the photo acoustic spectrum， and the correlation coefficient reached 0.91. Finally， the actual field measurement has been carried out to monitor the two non-uniform emission sources caused by different fertilization methods to achieve accurate measurement. It has practical engineering value such as agricultural gas emission and environmental gas detection.