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The results of the research on fluidization of multi-solid materials in cold and hot models have been introduced. It turned out that the change graphs of the statistical characteristic of pressure fluctuation can be used for evaluate values of fluidization velocity. Index Terms—Multi-solid bed, Pressure fluctuation, Straw pellets combustion, Turbulent fluidization. I. I NTRODUCTION The technology of dedicated biomass combustion and coal and biomass co-combustion in a fluidized bed is increasingly applied aiming to achieve a better control over a combustion process with a simultaneous decrease in greenhouse gases, ash and sulfur oxides emissions into the atmosphere. Straw is one of the most easily available biomass resources and its energy utilization is also constantly expanding requiring longer transport distances of the material. This stimulates the production of straw pellets, with a bulk density of 650-750 kg/m³ over 100-150 kg/m³ of baled straw. Fuel combustion can be carried out in a co-fluidized or multi-solid fluidized bed of fine coal ash particles or straw ash and straw char particles loaded with straw pellets. A multi - solid fluidized bed is a circulating fluidized bed in which an entrained bed consisting of fine particles is transiting through a fluidized dense bed of coarse particles, i.e. a bubbling bed in the bottom of the riser (1)-(4). The value of the minimum fluidization velocity of particles forming the bed is required for the design of fluidized bed furnaces. However, as has been proven (5)-(14) it is not possible to apply the known method of a minimum fluidization velocity evaluation from the pressure drop through a bed versus gas flow rate curve for a confined, multi solid or binary particle mixtures fluidized bed. The purpose of the present study is to define a method for the experimental evaluation of the minimum fluidization velocity of a bed compounded of fine and coarse particles mixtures at room and elevated temperatures.