The basic structure of White cell is introduced.And the influence of light reflection times of White cell system in gas monitoring is analyzed as an equally important factor.On this basis,a fiber coupling structure of White cell with long optical path is designed combined with the light coupling characteristics of fiber collimators.As a result,12 m absorption length is obtained on a 20 cm basic sized White cell and the light coupling efficiency of the system is steady at 55% or more in the certain temperature range.The White cell gas sensor can be applied for reote and on-line monitoring of the harmful gas remotely and on-line.