In order to solve the online inspection problem of paper moisture rate technical specification, the moisture rate measuring technique based on the near infrared spectroscopic analysis is researched. The basic theory on the spectral absorption of medium is expatiated and the problems applying the theory to the moisture rate measurement are also analyzed. The key technique that can realize the moisture rate on-line inspection by means of two near infrared spectral lines (measuring spectral line and the reference line) is explored in detail. The measurement project is designed and the role of the main functional module in the project is discussed. The corresponding experimental research showed that, the precision of moisture rate measurement based on near infrared spectroscopic method is less than0.5%. It is higher than measuring precision of the dry method and the method can be applied to on-line inspection in paper-making process.