The invention relates to a process for strengthening the bulging of external fluid replenishing hydraulic of a protective ring of a turbine generator, which is applied to the turbine generator field. High-pressure liquid produced by an external high-pressure pump passes through a passage of a high-pressure cylinder and is injected into a closed space formed by a upper fixed cone mould, a lower movable cone mould and the protective ring by a passage in a force-reduction column of a mould part in order that the protective ring generates plastic deformation under the action of hydraulic pressure, thereby achieving the aim of strengthening the protective ring; through adjusting low pressure of liquid in a low-pressure cylinder, the stress size of a contact part between the protective ring and the mould is adjusted so as to achieve the aim of sealing and adjusting the shape and the size of the protective ring; and a displacement sensor is used to monitor the bulging size of the protective ring. The process no longer occupies large-scale hydraulic press equipment, uses a load-bearing frame with a simple structure and small dimension and an external liquid replenishing cylinder to replace a hydraulic press for strengthening the protective ring; the bulging process can substantially reduce force, is easy to control the forming process, can repeatedly bulge, greatly improve the forming precision of the protective ring and reduce the machining allowance by 1/3 than the routine common hydraulic bulging; and the mould has a simple structure, convenient mounting and detachment, strong universality and low production cost and can achieve higher economical benefit.