Diamond wire saw was a tool which is used to cut the steel-based material, its grinding mechanism was researched in the paper. Based on technical characteristic of the diamond wire, a string of diamond beads in the cutting moment was detected by using the electron microscope. Wear figuration and invalidation reason of the diamond beads was analyzed, and mathematic relation among wear rate, feed velocity and cutting velocity of the diamond wire were educed, and reasonable cutting parameters were received. In order to validate the mathematic model, the experiment was finished. When the diamomd wire saw is used to cut the steel-based material, its two experiential formulas of radial feed force and tangent cutting force are educed by using the orthogonal regression method. In the formula, radial force and cutting force is increasing with augment of the workpiece breadth, ridial feed velocity and cutting velocity, and influence of the workpiece breadth to the cutting force is more than to the radial force. Meanwhile, experiment show yet that error between theory cutting(or feed) force and actual cutting(or feed) force is in the reasonable scope.