Abstract: Avalanche photodiodes (APDs) have been widely used in high bit rate, long-distance optical fiber communication systems because of their high sensitivity and gain bandwidth. The excess noise generated in the avalanche process has a significant impact on the sensitivity of APD. Therefore, the study of excess noise is crucial for the improvement of APD performance. The existing methods for testing excess noise of avalanche photodiodes primarily include direct power measurement and phase-sensitive detection. This article briefly introduces these testing methods, analyzes their advantages and disadvantages, and summarizes the state-of-the-art testing methods. Additionally, three methods to reduce excess noise are summarized: choosing materials with low impact ionization coefficient, using relaxation space to change the thickness of the multiplier layer to reduce the number of impact ionization of carriers and engineering the APD for appropriately heterogeneous impact ionization.