With large sample size and slight disturbance of sample’s original structure, a large scale in-situ direct shear test is an effective method for obtaining the strength parameters of material in geotechnical engineering. After investigating a set of direct shear apparatus for field and laboratory tests, a set of large scale in-situ direct shear apparatus is developed by Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. The apparatus is different from the traditional in-situ direct shear apparatus. It has an upper rigid shear box and a lower one, and is competent to conduct in-situ direct tests on soil sample with size of 50 cm×50 cm×41 cm and the largest grain size of 5 cm. It is convenient for assembly and suitable for complex field test environment. It can collect data automatically with a high precision sensor. This paper introduces the configuration, operation principle and technical advantages of the improved apparatus and describes the usages and problems encountered during testing on site in detail. The apparatus is applied to field tests of two landslides on Xiangjiaba reservoir to obtain the in-situ shear strength parameters of soil. Through analysis of shear strength curves for different samples, the apparatus is verified to have excellent performance.