Window milling method for casings of continuous oil pipes

The invention provides a window milling method for casings of continuous oil pipes. The window milling method includes steps of a), carrying out operation for drifting the diameter sides of the casings and scraping the inner walls of the casings so as to prepare well bores; b), setting positioning assemblies in the casings, to be more specific, setting the positioning assemblies in wellheads, descending the positioning assemblies to preset positions in the casings and then setting setting apparatuses of the positioning assemblies on the inner walls of the casings; c), fixing whipstock in downhole environments, to be more specific, setting the whipstock in the wellheads and inserting whipstock assemblies of the whipstock into the setting apparatuses; d), carrying out casing window milling, to be more specific, setting window milling cones in the wellheads, descending the window milling cones to reach the whipstock assemblies and starting the window milling cones to carry out window sidetrack drilling on the inner walls of the casings. The window milling method for the casings of the continuous oil pipes has the advantages that the directions of oblique planes of the whipstock can be accurately adjusted, and the window milling method is easy and convenient to implement and is safe and reliable.