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Abstract. HTS tapes production technology has reached the level which allows the manufacture of high-quality cables of long length. In this connection, the issue of creating an HTS power transmission line of some kilometer length had been raised. Pressure loss appears as one of the limiting factors in the circulation of the liquid nitrogen cooling HTS cable placed in a long cryostat. Pressure loss is small in short lines and for this reason did not attract close attention of researchers until recently. Within the framework of the Russian R&D program for HTS power devices, 30 and 200 m AC HTS power transmission lines were created in 2008 and 2010, respectively, and a new 2.5 km 50 MW DC line to be installed in a real city network of St. Petersburg is now at the design and development phase. Pressure loss calculations show the 64/70 mm NEXANS-type corrugated flexible cryostat to be optimal for the cooling channel and the 39/44 mm one -for the return channel. In this case, it is possible to use just one cryopump and one cryocooler to achieve an operational temperature difference of 4-6 K and a pressure drop of 0.1-0.2 MPa in the cooling channel at a flow rate of 20-30 l/min.