The invention provides a hydroxy modification method for a low-pressure microwave radiation carbon nanometer tube, it relates to the hydroxy modification method of the carbon nanometer tube and solves the problems of the existing modification technology on nanometer tube that the technical process is complex, the reaction time is long, and the energy consumption and the cost are high. The modification method includes the steps of: 1. soaking carbon nanometer tube into alkali solution, then heat by microwave under low pressure, and remove the upper layer of alkali solution after the cooling and precipitation to obtain the precipitate; 2. cleaning and dry the precipitate to obtain the hydroxy-modified carbon nanometer tube. The invention greatly shortens the reaction time and has the advantages of simple technique, low energy consumption and low cost.