A sample analyzer with an optical detection device and a sample analysis method of the sample analyzer are disclosed. The optical detection device includes a fluid chamber, a light source and a light detector. The fluid chamber includes an illumination zone. An analyte flows through the illumination zone so as to form a sample stream. The light source illuminates the illumination zone to excite cell articles, reacted with a reagent, of the sample stream to emit a light signal. The light detector detects the fluorescent lights and transforms it into an electric signal. The light detector can include a silicon photomultiplier.