Abstract: Mature Ceratophyllum demersum was planted in the turbid solution with different turbidities of 30 NTU,60 NTU and 90 NTU.The turbidity was caused by suspended substance.For determining the influences of turbidity on the photosynthetic fluorescent characteristics rapid light curves(RLCs) were determined.The experimental results demonstrated that in 60 and 90 NTU turbid solutions fluorescence yield(F_t),maximum light-adapted fluorescence yield(F′_m) and ΔF_v/F_m were less significantly than those in the control and 30 NTU solution.Compared with the control plants,photochemical quenching(qP) and non-photochemical quenching(qN) notablely decreased with light exposure of a leaf increasing in turbid solutions.It indicated that photosynthetic capacity and activity of non-photochemical quenching pathways were remarkably reduced.In turbid solutions,the minimum saturating irradiance(E_k) and maximal relative electron transport rate(rETR_max) were less significantly than the control.These proved that their light responding capacity were reduced notably by suspended sands.So it isn’t good for C.demersum to(survive) in high tubidity of suspended sands solution.