The utility model discloses a simple auxiliary device of a traditional jet fan for a tunnel. Four fixing screw caps are uniformly distributed and welded on the jet fan; the annular fan sleeve is arranged on an air outlet of the jet fan through a telescopic rod; two common screws abutting against the jet fan are installed in the fixing nut. A first upper connecting plate is welded at the upper partof the annular fan sleeve, and a first lower connecting plate is welded at the lower part; tubular nylon cloth is arranged on the annular fan sleeve; strong-viscosity tinfoil covers the interior of the tubular nylon cloth; the tubular nylon cloth is in reverse buckling connection with an annular clamping groove formed in the annular plastic pipeline; a second upper connecting plate is arranged onthe upper portion of the annular clamping groove, a second lower connecting plate is arranged on the lower portion of the annular clamping groove, an adjustable connecting rod and a common screw arearranged between the first upper connecting plate and the second upper connecting plate, and a specially-made screw and a common screw are arranged between the first lower connecting plate and the second lower connecting plate. The device is simple and convenient in structural design, easy to mount, dismount and use, convenient to operate and low in time consumption.