Annular shield machine and tunnel construction method

The invention relates to an annular shield machine which comprises a shield housing, a duct piece traction mechanism and a turbid water delivery system, wherein the shield housing comprises an outer housing, an inner housing and a small shield housing; the inner housing, the small shield housing and the outer housing form an annular cavity; small cutting heads are distributed along the circumferential direction of the annular cavity; a primary cutting head is arranged in the small shield housing; the primary cutting head is communicated with the inner housing; and a shield jack is arranged behind the small cutting heads. The invention also provides a tunnel construction method. The annular shield machine disclosed by the invention has the characteristics of safety and reliability, simplicity and convenience, high efficiency, economy, environment friendliness and the like. By using the novel tunnel construction method disclosed by the invention, excavation can be carried out at any tunnel lining part in any shape, then earth and sand are excavated in the constructed tunnel lining, and finally the tunneling is completed.