Abstract: Low temperature in deep water drilling makes the wellbore temperature distribution different from that in onshore wells,and the fluid in boost line makes the wellbore temperature lower.So it is necessary to understand the effect of the flow rate in boost line on borehole temperature distribution.Based on the calculation method of deep water temperature field without boost flow in riser,the wellbore fluid temperature field in deep water drilling with boost flow in riser was studied while considering the issue of expansion channel flow and combining related theories of thermodynamics,and the method to predict temperature field was established.The results showed that boost line had significant influence on the distribution of wellbore fluid temperature in deep water drilling with large influencing range,the boost line had more obvious influence comparing with pipe string,the influence of boosted flow on drilling fluid temperature was even deep into the formation resulting from different level of drilling fluid in annular and string.Therefore,the influence of boosted flow must be considered in deep-water temperature distribution in deep water drilling.