This paper makes a comprehensive study on the triangulation of ADS40 airborne three line images supported by GPS/IMU data. Considering that different Local Space Rectangular (LSR) systems have been adopted for different ADS40 strips, the equations to transform the exterior orientation elements of all ADS40 strips to one LSR frame are derived at first, then the principle of the block adjustment of three-line image using orientation image is introduced and a math model to describe the error of IMU/DGPS data is designed. Two datasets from Waldkirch test field located in Switzerland, which have been acquired in May 2002 with the GSD of 20cm and September 2004 with the GSD of 35cm respectively, are used to test the correctness of algorithms mentioned above. Block adjustment experiments have been carried out for the blocks constructed by all west-east strips and plus two cross strips at each end of them. Results indicate that the positioning accuracy of IMU/DGPS data can be promoted effectively when only one ground control point is introduced into adjustment. While locating one control point at each corner of the block, the combined adjustment of IMU/DGPS data with ADS40 image observations achieves the accuracy of 1.5 pixels on the ground. The cross strips are not good for combined adjustment and not recommended in actual application.