Objective To study the effect of silica in soil on the extraction of biological evidence DNA at the crime scene using the silica bead method.Methods Mud suspension and diluted blood were mixed to prepare biological samples mixed with dust and soil,which is to simulate biological evidence at the crime scene.Cell lysis was performed using heating lysis and guanidine salt chemical lysis,respectively.DNA was extracted using the silica bead method,amplified by PCR using Identifiler Plus kit and detected by capillary electrophoresis.The electrophoresis results were compared.Using mud suspension instead of silica beads to extract diluted blood DNA to validate the effect of silica in soil on the extraction of biological evidence DNA at crime scene using silica beads method.Results The complete STR loci were obtained after the extraction and amplification of 4 μL,20 μL dilute blood mixed with mud and lysed with heating cracking,whoes average peak heights arel 969.7±376.9 RFU and 9 706.7±349.8 RFU.For the 4 μL dilute blood mixed with mud guanidine salt chemical lysis,it cannot obtain complete STR loci after extraction and amplification.20 μL dilute blood mixed with mud guanidine salt was chemically cleaved and amplified to obtain complete STR loci with an average peak height of 1 899.8±801.3 RFU.After extraction and amplification by mud suspension instead of silica beads to extract 20 μL diluted blood DNA,complete STR loci were obtained.Conclusion Silicon dioxide in soil can bind to DNA in the presence of guanidine salts,leading to a decrease in the efficiency of recovering on-site biological evidence DNA using the silicon bead method.