The theory and model of multiple stable states in shallow lakes were improved on the basis of researches in Taihu Lake and other similar lakes. This paper presents the outline of a conceptual model for multiple stable states in shallow lakes. The model is composed of two curved surfaces in a three-dimensional space. The first dimension is external nutrient load of the lake (ENL) which acts as themain forcing factor in eutrophication process of lake ecosystem. Water nutrient level (WNL) takes the second dimension. The third one represents relative dominance of macrophyte and phytoplankton (RD). The upper surface is macrophyte-dominated clear-water phase, and the lower surface represents phytoplankton-dominated turbid-water phase. The two phases are divided into six states (S₁-S₆) by the critical values a and b on the WNL dimension. When WNL < Ca, there is only one stable state, macrophyte-dominated clear-water state S₁. Some biologic or environmental factors may keep the lake water at a turbid state*sub-stable state S₄. If those factors are removed, the system will automatically turn to S₁ state. When a < WNL < b, two stable states S₂ and S₅ may exist. The S₂ state may be kept by aquatic macrophyte for its positive effects on the water quality and inhibition effects on phytoplankton. If macrophyte is destroyed for any reason? the system may irreversibly skip to S₅ state, phytoplankton-dominated turbid-water state. To restore the system back to S₂ state, great efforts is needed from the human being. When WNL > b, there is only one permanent stable state, phytoplankton-dominated turbid-water state S₆. An unstable state S₃ may exist if b < CWNL < Cc. but macrophyte dominance will be automatically replaced by phytoplankton dominance in a short time. When WNL > b, any attempt to restore the system by biomanipulation will be infructuous. With the guiding of this model.state succession process in each basin of Taihu Lake is analyzed. Experiments were carried out to protect East Taihu Lake from algal-dominance and to restore other basins.