Abstract: The underwater light environment has an important influence on lake ecosystem and is an important factor limiting the growth and development of submerged plants.Studying the attenuation characteristics of photosynthetically active radiation(PAR) is of guiding significance for the recovery of submerged plants in lakes.This study investigated the spatial and temporal characteristics of PAR in Caohai Lake from March to August in 2022.The relationship between diffuse attenuation coefficients of photosynthetically active radiation(Kd(PAR)) and total suspended solid(TSS),inorganic suspended solid(ISS),organic suspended solid(OSS),chlorophyll-a(Chl.a) and chromophoric dissolved organic matter(CDOM) were studied.The results showed that the average Kd(PAR) during the period from spring to summer was(2.90±1.12) m-1,and the average of Zeu was(1.84±0.69) m.The concentration of TSS,ISS,OSS,Chl.a and CDOM absorption coefficient was(20.11±4.76) mg/L,(8.68±4.91) mg/L,(11.66±12.43) mg/L,(21.88±8.49) mg/m3 and(3.11±0.68) m-1,respectively.In Caohai Lake, Kd(PAR) in northern waters was greater than that in southern waters.The Kd(PAR) was significantly correlated with TSS(P<0.01),ISS(P<0.01) and turbidity(P<0.001),but was not significantly correlated with Chl.a(P>0.05).The dominant factor affecting Kd(PAR) in Caohai Lake in spring was ISS,and the factors in summer were dominated by ISS and CDOM.Taking the spring and summer as a whole, the factors affecting Kd(PAR) were dominated by ISS and Chl.a.,indicating that the dominant factor of Kd(PAR) in Caohai Lake was suspended material, which was mainly due to sediment resuspension caused by wind and waves after the decline of aquatic plants.In addition, the increase of CDOM and Chl.a concentration were also key factors affecting Kd(PAR).In this waterbody, average value of euphotic depth(Zeu) was greater than the average of water depth, indicating that the light environment was favorable to the growth and development of submerged plants.However, water suspended material content was high in Caohai Lake, and its coverage can limit growth and development of submerged plants, which may be an important reason for the unsatisfactory recovery of submerged plants after lowering water level.