The invention relates to a detection method for the cross section of a 
fiber. The detection method comprises the following steps: 1, horizontally laying the 
fiber on a film, sticking two 
metal plates between the 
fiber and the film, fixing the two 
metal plates, 
drying, cooling, carrying down the fiber from the film to obtain an impression picture of the longitudinal cross section of the fiber on the film; and 2, adhering the fiber to the bottom of a container by an 
adhesive, adding a resin mixture to the container, 
drying to polymerize the resin mixture, cooling at 
room temperature, 
slicing toobtain a slice, adhering the slice to a slide glass, and putting the slide glass in 
cedar oil for the 
microscope observation. The detection method of the invention has the advantages of simplicity, no new 
equipment requirement, and realization of the large scale application. Compared with the direct 
microscope observation, the method of the invention allows the obtained field depth to be better, complete information of the cross section of the fiber to be once obtained, and influences of dyes of the surface of the fiber to be eliminated, so the discrimination accuracy on the fiber is improved.