A method based on the light-blocking theory for detecting impurity particle signals in ampoules was introduced. The optelectronic characteristics of signals of particles contained in ampoules were investigated and analyzed. First, the characteristics of the signal of the pulse amplitude were calculated and simulated based on the scattering theory and large particle light-blocking conditions, respectively. Next, the impact factors of particle diameter, area of detector, beam width and wavelength were investigated. In addition, in order to improve the accuracy of the test results, an optimized optical layout based on lens array and photodiode array was proposed and confirmed by experiment.