The invention discloses a preparation method and a product of a polytetrafluoroethylene (PTFE) film. The preparation method comprises the steps of: mixing PTFE resin powder with a liquid lubricant, extruding, calendering, longitudinally stretching, laterally stretching and heat setting, and rapidly spraying cooling water under certain pressure to obtain a bidirectional stretched PTFE microporous film with the micropore aperture of 0.2-10, the lateral shrinkage of smaller than 3%, and the longitudinal shrinkage of smaller than 5%. The PTFE film has stable lateral and longitudinal dimension, great improvement of film usability, simple process and low cost.