A new method of using object-surface single-mirror wave front-division threebeam holographic interferometry to measure 3D displscement field of an object is proposed.In this method,a small mirror is sticked to the surface of the measured object,then the three independent double-exposure interferograms of the measured object are recorded in three different parts or identical region of the holographic plate with the help of three diverging beams.The interferograms are modulated by the displacements of the virrual point sources of the reference beams due to motion of teh small mirror. Based on theoretical analysis to this modulation phenomenon, two sets of linealy equations for computing 3D displacement of the virtual point sources of the reference beams and the measured object have been derived. The experimental resualts have been given.