By investigating a bilayer gastrointestinal normal tissue (including mucosa and submucosa layers) and a cancerous tissue model (including adenoma and submucosa layers), the laser-induced autofluorescence (LIAF) spectra by Monte-Carlo simulation are reconstructed. The good correlation between the reconstructed spectra and experimental spectra suggested that Monte-Carlo simulation can accurately describe the generation and transportation of fluorescence in tissue and therefore can detect cancerous tissue by revealing the real biophysical and biochemical information of tissue.