The invention discloses a stable control device of thermal parameters of the secondary side of a compact steam generator. The stable control device comprises a water storage tank, wherein the water storage tank passes through a high-speed centrifugal pump, a vertical preheater and a regulating pipeline in sequence through pipelines and then enters a water supply inlet of the secondary side of the steam generator, and a steam outlet of the secondary side of the steam generator passes through a condenser through a pipeline and then returns to the water storage tank. According to the stable control device, a large-flow adjustment branch and a small-flow adjustment branch are arranged on an output pipeline of the high-speed centrifugal pump, pneumatic switching valves are controlled to select according to the range of flow during actual operation, and multistage throttle hole plates are respectively arranged on each branch, so that the pressure difference of steam between an outlet of the centrifugal pump and the outlet of the secondary side of the compact steam generator is increased and is at least greater than 0.4 MPa, the phenomenon of flow instability of the secondary side of the compact steam generator is avoided, and the stable control over the water supply flow of the secondary side is realized.