In the drilling of mud shale formation，the shale is very easy to absorb water and expand，resulting in block falling and collapse of well wall. Therefore，the well wall needs to be reinforced during drilling process. Simulating the biomineralization deposition process，nanoparticle and cationic polymer were alternately deposited on the surface of silicon wafer to form nano mineralized deposition layer. Nanoparticle and cationic polymer were optimized. The surface and cross-section morphology of deposited layer were analyzed by atomic force microscope and scanning electron microscope. The composition of deposited layer was analyzed by infrared spectrometer，and the mechanical properties of deposited layer were studied. The results showed that the deposition effect of nano calcium carbonate was better than that of nano silica，and the deposition effect of nano calcium carbonate with low concentration was excellent. A uniformly dispersed，dense and firm“mud brick stacking”structure was formed after silicon wafer deposited alternately in 1% cationic polymer（branched polyethyleneimine）and 0.4% nano calcium carbonate. When the number of deposition cycles reached 25，the thickness of deposition layer was 23.88 μm and the transverse tensile Young’s modulus was 1.4086 MPa，showing good viscoelasticity. Modified nano calcium carbonate and cationic polymer could form a dense and stable sedimentary layer on the simulated well wall，which provided a new idea for strengthening and improving the stability of well wall.