We investigated the effect of operation conditions on bio-oil yield in Hydrothermal Liquefaction (HTL) of Cyanophyta to produce bio-oil. The experiments were carried out at different reaction temperatures (280-350 degrees C), retention times (15-60min), algae/water mass ratio (0.1-0.3) in 2.7mL batch reactors. In the testing temperature and time range, the bio-oil yield increased first then decreased, respectively. The maximum bio-oil yield of 49.40% was obtained at reaction temperature 350 degrees C, retention time 30min, algae/water mass ratio 0.1 and 18MPa. Higher temperature and algae/water ratio would lead to higher light biocrude yield but lower bio-oil yield and heavy biocrude yield. The impact of operation parameters on solid yield was small in general. GC-MS analysis showed that the light biocrude might contain methylic or methylene alkanes, phenols and its derivatives, benzene and homologs of benzene, ketones, acids, esters, amides, amines and alcohols.