Based on the self-made “black box” experimental device, this paper verified the relationship between saturated photocurrent and light intensity by three methods: The first method is to study the volt-ampere characteristic curve under different light intensity by controlling the voltage of the phototube; The second one is to study the photoelectric characteristic curve of photocell by changing the distance between phototube and light source under the same light intensity; And the third one is that the relationship between photocurrent and light intensity can be directly measured by using light intensity sensor. The experimental data were collected and analyzed by PASCO platform in real time. When the saturation was not reached, the experimental results show that the photocurrent increased with the increase of light intensity.