The invention relates to a method for preparing a large-size low-water-peak prefabricated rod, which comprises the following steps of: 1, depositing a core layer and partial cladding material in a
quartz glass lining tube by using an in-tube
chemical vapor deposition method to meet the requirement of a
waveguide structure and optimize
fluorine doped components, wherein the F-doped
refractive index contribution of an inner cladding layer prepared by an in-tube method is not more than -0.10 percent and the F-doped
refractive index contribution of the core layer is not more than -0.03 percent; 2, melting and shrinking the
quartz glass lining tube deposited with the core layer and the partial cladding material at the temperature of between 1,900 and 2,300DEG C into a
solid core rod, and manufacturing a core rod of which the b / a is more than or equal to 1.5 and less than or equal to 3.0 and the c / a is more than or equal to 2.3 and less than 4.5; 3, cladding a proper amount of uniform
quartz loose body on the outer surface of the core rod directly by using an outside vapor deposition method to obtain a loose body prefabricated rod; and 4, slowly heating the loose body prefabricated rod at high temperature for
dehydration, and
sintering to obtain the transparent large-size low-water-peak prefabricated rod. The
advantage of
doping of the in-tube method and the
advantage of
large size of the outside method are combined, the process is simple, and the method is suitable for producing large-size low-water-peak prefabricated rods at low cost on a large scale.