A testing system measures central angles of filter segments of a color wheel. The color wheel includes a color filter, which includes three sector-shaped filter segments and a motor for driving the filter segments to rotate. The testing system includes a sensor and a processor. The sensor emits light toward the color filter and receives light reflected back by the color filter, and generates an impulse signal according to intensity changes of the light reflected back by the color filter. The impulse signal includes a plurality of boundary impulses corresponding to boundaries formed between adjacent filter segments. The processor calculates central angles of the filter segments according to relationships between the boundary impulses.