The invention relates to an online measurement device and method for boiler pulverized coal particle parameters. The device comprises an optical signal collection unit and a data processing unit, wherein the optical signal collection unit is used for collecting an optical signal caused by that pulverized coal particles flow through a measurement area, and comprises two paths of light sources, probes and a photoelectric element, the light sources are used for emitting light to irradiate the measurement area, the two paths of probes are inserted into a boiler pulverized coal particle pipeline, the photoelectric element is used for receiving the optical signal of the pulverized coal particles flowing through the measurement area and converting the optical signal into an electrical signal, the data processing unit is connected with the optical signal collection unit, and is used for processing the signal collected by the optical signal collection unit, the data processing unit comprises a data collection system and an analyzing and processing system, the data collection system is used for recording and storing the signal collected by the optical signal collection unit, the data processing unit is used for processing the signal recorded and stored by the data collection system, and a processing result is stored in the data collection system. The online measurement device and method have the advantages that a structure principle is simple, the sensitivity is high, and the like.