The invention discloses a rainfall measurement apparatus. The apparatus comprises a box body, a rainwater collection portion, a water leakage port, an optical fiber sensor, an optical fiber float, a slide bar and a drain plug. The slide bar is fixed to a bottom in the box body. The optical fiber float is arranged on the slide bar. The optical fiber float slides up and down along the slide bar under an effect of buoyancy of water in the box body. An optical fiber tail end of the optical fiber sensor is fixed to the optical fiber float and generates a curve along the slide of the optical fiber float. The optical fiber tail end of the optical fiber sensor is plated with a film with a high reflectivity. The bottom of the box body is provided with a water outlet. The drain plug matches with the water outlet and is arranged on the water outlet. A top of the box body is provided with a water leakage port. The rainwater collection portion is connected to the box body through the water leakage port. The invention also discloses a rainfall measurement system and a method. In the invention, based on a plastic optical-fiber curved characteristic, the rainfall measurement is performed, and reliable, accurate, economic and automatic rainfall acquisition and measurement in a timing mode can be performed in a severe environment.