The electrospun microfibers of high-viscosity polyacrylonitrile (PAN) solution possess stronger tensile strength, but poor electrospinnability. Sonication treatment was introduced to improve the electrospinnability of highviscosity PAN solution. The influences of sonication time on the solution properties, including dynamic rheological properties, electric conductivity and surface tension, as well as the deformation of Taylor cone and electrospinning jet whipping behavior were investigated. The surface morphology of the resultant fibers was observed using scanning electron microscope, and the mechanical properties of the fiber mats were measured through tensile test. The experimental results indicated that the electrospinnability of the PAN solution was significantly improved by the sonication treatment due to the improved rheological properties, increased electric conductivity and reduced surface tension. It was also found that sonication treatment could elongate the Taylor cone and drastically intensify the whipping instability of the electrospinning jet. When the solution was treated for 4 min (720 W), the average diameter of the obtained electrospun PAN fibers reduced from 3,180.46 to 2,657.23 nm as the unevenness rate reduced from 16.38 to 15.27 %. The tensile strength of microfiber mats increased from 2.50 to 6.61 MPa, showing an increment of 164 %, while the Young's modulus is strengthened fivefold, increasing from 39.49 to 248.97 MPa.