A symmetrical direct shear apparatus for in-situ testing of pile-soil interface shear strength comprises a support (1). Two shearing devices which are symmetrically distributed are disposed on the support (1), and each shearing device comprises a shearing box (11), a fan-shaped distribution type normal force provision mechanism used for applying normal force to a soil sample (100) in the shearing box (11), a shearing displacement measurement mechanism used for measuring the shearing displacement of the shearing box (11), and a counterweight (16) used for applying shearing force to the shearing box (11). A method for in-situ testing of the pile-soil interface shear strength. Uniformly-distributed normal force is applied by using the fan-shaped distribution type normal force provision mechanism, without externally connecting a pressure source or loading device; the magnitudes of the normal force at various points of the interface are the same and point to a circle center by applying the normal force by means of the fan-shaped distribution type normal force provision mechanism in the center of a sample, so that a shearing surface is uniformly stressed, and the deviation of test results caused by the fact that the sample is eccentrically loaded is avoided.
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