Echelle spectrograph has two-dimension spectra on the image plane for its cross-dispersion structure, which makes it hard to design and analysis. In order to overcome these difficulties, an efficient algorithm based on the limits of boundary is described. The mathematic model is developed between the system requirements, structure parameters and two-dimension echelle spectra. This algorithm can obtain the echelle spectrograph parameters quickly according to the system requirements, and establish the echelle spectra using these parameters, and then the parameters are modified according the results of echelle spectra, which provide a valuable method for designing echelle spectrograph and analysing spectra. Utilizing this model an echelle spectrograph is designed with the wavelength range of 200~900 nm and the spectral resolution of 25000 at 200 nm. After the measurement, this configuration can meet the needs of system.