The invention relates to a well completion and oil production string of a horizontal well and well completion and oil production processes. In order to overcome the defect that in traditional horizontal well open hole sand-proof screening pipe well completion construction, an open hole packer at a horizontal section cannot effectively seal and separate oil and water layers because of irregular well diameter, a well completion string is fixedly arranged at the horizontal well section in an open hole well bore; a grading hoop, a casing short section, an external casing packer I, a blind plate, a casing, a layered seal tube I, an upper screening pipe, a layered seal tube II, a second casing short section, an external casing packer II, the other casing, an external casing packer III, a third casing short section, a layered seal tube III, a lower screening pipe, a wash-down valve, the lower screening pipe and a guiding shoe of the well completion string are sequentially and fixedly connected; and an acid washing string, a string for sealing up and producing oil from down, a string for sealing down and producing oil from up or a commingled production string is arranged in the well completion string. The invention has the beneficial effects that the well completion process of the horizontal well is combined with a post oil production technology, the sectioned sealing effect between the well completion string and the open hole well bore is improved, bottom water coning is delayed, and the purposes of controlling water and increasing oil are achieved.