Chang 3 reservoir in Hua 152 block is located in the Ordos basin, China. The average permeability and porosity is 3.17mD and 14.9%. There exists serious scaling at the oil layer near to bottom hole because of high salinity formation water and incompatible injection water. The scaling process and mechanisms in the layers has been researched by means of a visual real-sand micro-model. The results have shown that: 1) The permeability of the oil layer will reduce by 40% when formation water contacts with injection water twice times at the same place; 2) It is very easy for scaling molecules to crystallize from water phase and scale particles are very small because the pores and throats of the formation rock contain a lot of fine clay and impurity; 3) The scale accumulates in pores and looks like "chicken roost"; 4) The scale inhibitors can reduce scaling, but the higher concentration of scale inhibitors is needed. Scaling in low permeability reservoirs may significantly reduce rock permeability thus affecting the production of oil well. The visual real-sand micro-model is a good method to use in research of scaling mechanisms because of its visualization, using actual rock and ease of construction.