Methods for determining the degrees of fiber formation of textured vegetable proteins are provided. One inventive method based on fluorescence polarization technology comprises selecting a sample or a section thereof, using fluorescence polarization spectroscopy to detect P-value or Anisotropy Index of the sample, and obtaining the degree of fiber formation by comparing the P-value or Anisotropy Index to a pre-generated database collating P values or Anisotropy Index with degrees of fiber formation. Another inventive method based on image processing technique comprises preparing a sample to reveal its fibrous structures, obtaining an original image of the sample, applying edge detection to the original image to produce a second binary image with enhanced contrast, performing Hough transform on the second image to extract line information and generate a third image; defining region of interest on the third image; calculating the degree of fiber formation though analysis of the region of interest. The invention also combines the aforesaid methods to enable the automated and real-time determination of the degree of fiber formation of textured vegetable protein during a production line.