The particle mixer has a wide application in the chemical and petrochemical industries. In order to achieve adequate and homogeneous particle mixing, a new type of particle mixer was proposed by coupling a pre-mixing section and an internally circulating fluidized bed mixing section. The bed density and particle circulating velocity, as well as the cold and hot particle mixing degree in the mixer were investigated with an optical fiber probe and thermal particle tracer technology. Bed density in the internally circulating fluidized bed mixing section decreased with the increase of the superficial gas velocity in the draft tube, but changed slightly with the rise of the particle feeding mass flow rate. The radial evolution of the dimensionless bed density in the draft tube was approximative under different operating conditions. With the increase of the superficial gas velocity and particle feeding mass flow rate, both the particle circulating velocity and circulating mass flow rate increased, within 0.23 to 0.28 m/s, and between 90 kg/(m(2) s) and 10 kg/(m(2) s), respectively. The mixing performance was improved as the superficial gas velocity increased, while it changed only slightly with the rise of he particle feeding mass flow rate. The radial particle mixing was significant in the pre-mixing section where the mixing index could reach 0.7, and then in the draft tube where the mixing index could reach 0.95.