BT-90 dynamic light scattering nano particle size analyzer is a research result of South China Normal University which introduced by Bettersize Instruments Ltd. It is a project of industrialization implemented by both sides. This instrument adopts dynamic light scattering theory. When laser beam irradiates nano particles, pulsate scattered light signals will be occurred. Rate-of-changes of signal intensity and frequency are related to motion state (speed and amplitude) of particles and motion state is related to particle size. Hence, photomultiplier is used to receive these pulsate signals of scattered light, and these signals will be processed by digital correlator so as to recognize effective light scattering signals. Through inversion processing of special software, particle size of particles in nanometer as well as its distribution will be calculated by Stokes-Einstein formula. The instrument can test wide distribution samples in nanometer, which has the characteristics of easy operation, high precision and wide test range, etc. It applies to the fields of production, scientific research and teaching of nanometer materials.