The embodiment of the invention provides an internal dewatering and drainage construction method for a tunnel passing through a water-rich unconformable contact zone and relates to the field of building construction. The method can safely and quickly complete internal dewatering of the water-rich tunnel and can guarantee engineering quality and construction safety. The method comprises the following steps: determining a lower-side heading position according to a water incoming direction; setting out and conducting lower-side heading dual-drainage small conduit advanced supporting; arranging deep drainage holes in the face of the lower-side heading for water drainage; excavating and supporting the upper part of the lower-side heading; excavating and supporting the lower part; arranging internal drain pipes at the excavated section; conducting radial well hole construction of the rest section in the lower-side heading and draining water; gathering underground water and pumping the water to the outside.