Dynamic mechanical automatic vertical drilling tool is widely used in vertical well operations. Improving its restoring performance is the key goal of optimizing drilling tool. The opening angle of upper disc valve in the stable platform has a great influence on the restoring performance. In view of this, three indexes of expansion force impulse, guiding force impulse, abrupt transition amplitude and fluctuation amplitude of guiding force were set up to evaluate the degree of borehole helix, effective push force and stability of guiding force, and to evaluate the restoring performance of drilling tool at different opening angles of upper disc valve. By analyzing the state of the drilling tool in the restoring process, the changing rule of the resultant force of outstretched hands was obtained, and compared with the test value. Finally, the changing rule of the three indexes at different opening angles of upper disc valve was obtained. The results showed that the theoretical value of the resultant push force was close to the test value. When the opening angle of upper disc valve was 180°, the restoring process was stable and efficient, and the degree of borehole helix could be reduced to the maximum extent. Three proposed evaluation indexes and the research results provide a new idea for the following overall optimization design of the vertical drilling tool.