The time sequence of writing and seal formation was analyzed by microspectrophotometer, and the time sequence of different files was detected by using the transmission spectrum method in this experiment. Experimental results showed that the transmissions of samples from different time could be detected between 400 and 750nm. The values of the red seal mixed with the ink, the white paper and the writing pigment color were different. Compared with the characteristics of the sample photos, they could be distinguished effectively. The method was effective, accurate and was harmless to the samples. The time sequence of black pen or blue pen and seal formation could be identified effectively with the method.