The utility model relates to a transformer substation's cable pit optical cable seal groove, including the cell body, the cell body cross -section is half and surrounds the structure, recess that cell body left and right sides limit top was equipped with bilateral symmetry be used for with the cooperation of (b) optical cable capping realize sealed, thereby it makes things convenient for the cell body to carry out the drainage for 0.5cm's hole to offer a plurality of diameter in the bottom of cell body. 1, compressive capacity is strong for this cable duct, and the material is acidproof, alkali, salt corrosion behavior are good, and is difficult damaged, 2, the maintenance can conveniently be opened to this cable duct, the convenient cable of newly glitteing, 3, it is firm that optical cable seal groove junction is connected, and the optical cable is difficult exposed, 4, improve the efficiency of construction, prefabricated of the assembling, construction cycle is very short.