Xiaolangdi sand exclusion cave is the first case of hydraulic tunnel lined with double-ring surrounded non-bonded prestressed concrete in China, this paper gives a brief introduction to this new structural form and characteristics, and according to a large number of measured data obtained by the observation instrument, it discusses the effective prestressing force changes in the concrete lining and anchors in the different phases (prestressing force application, backfill grouting and over-water operation) and the change rule of concrete creep. The measured data show that the double-ring encircling unbonded prestressing technique can realize ideal prestressing effect and uniform ring stress distribution. The quality of the surrounding rock excavation has an important influence on the uniformity of the ring prestress distribution; for the actual structure that takes a long time to apply prestressing, the creep strain of the concrete occupies a non-negligible proportion in the total strain change of the observation instrument, and its size and the pre-compressive stress and the holding time are linearly related to the pre-compressive stress and the holding time, and can be measured by? =? ∑?iti can be calculated. The measured data of the over-water operation stage show that the precompressive stress established in the concrete lining of the project is sufficient to resist the internal water pressure at the maximum design operation level without cracking or seepage.