This paper determined the lethal concentration （LC） and hemi-inhibition concentration （HIC） of inorganic element Cu²⁺, Zn²⁺,Se⁴⁺,Cd² to the unicellular alga Platymonas helgolandica var. tsingtaoensis （cell density were 3.4× 10’cell/ ml ）, Phaeodaetylum iTⁿutum （cell density is 2. 7 × 10⁶ cell/ml） Dicrateria zhan jiangensis Hu （cell density were 5. 6 × 10⁶ cell/ml）, Paviova luther（cell density is 2. 7 × 10⁶ cell/ml）. The culture condition: temperature was 25±2℃, pH 7. 9± 0. 1, salinity 31±1.0,natural sunlight for 5 days. The different species unicellular alga with different absorbability to these inorganic elements were analyzed by Scanning Electron Microscopy X-ray Energy Spectrum.