In order to study the spatio-temporal patterns of cyanobacteria blooms, it is important to detect and monitor them effec-tively by satellite observations.However, such detection and monitoring by low resolution data induces a scaling bias.Based on MODIS(250 m and 500 m) data at Oct.17, 2005 and Dec.3, 2010, the area of cyanobacteria bloom in Lake Taihu was derived by a approach named Floating Algae Index (FAI).The low resolution FAI was then achieved in two ways:FAI₅₀₀, was directly calcu-lated from MODIS(500 m);and the FAI_mean was the mean of FAI₂₅₀ which was directly calculated from MODIS(250 m).Results reveal a serious overestimation of FAI₅₀₀ and the area of cyanobacteria bloom due to the scale error all over Lake Taihu.The causes for scaling error are discussed and it is found that the spatial heterogeneous is the key factor which may lead to the error in the de-tection and monitoring on cyanobacteria bloom.