In this paper，a kind of terahertz (THz)polymer tube is designed which has better transmission properties.The THz polymer tube has ideal S parameters，low transmission loss，and the transmission coefficient is above 0.96 with HFSS analysis.Nevertheless，there is mimicking surface plasma phenomenon in the field distribution of the THz polymer tube，which makes the transmission properties worse.And coated metal on the terahertz polymer tube outer or inner wall can restrain this phenomenon，which will make the field distribution more uniform and stable.Contrasting three coated pattern，the terahertz transmission characteristics of the inner coated THz polymer tube is the best，and polymer tube with inside and outside coat is the worst.Therefore，the coated pattern should be preferred to choose inner coated，which can simplify the process and reduce cost.