Abstract: Aiming at the problems of poor strength,prone cracking,and low gas sealing efficiency of traditional clay cement composite gas sealing materials (CCC),a new type of claycement based spraying material of gas sealing (XM-CCC) modified by xanthan gum (XG) and magnesium oxide (MgO) was prepared.Through water separation proportion test,slurry time varying and rheological tests,the best water solid ratio of 0.6 and the best clay content of 20% were determined.Through mechanical performance test and constrained expansion test,the optimal amount of XG 1.5% and MgO 5% were determined.The compressive strength of XM-CCC (7 d) reaches 25.33 MPa,the flexural strength reaches 9.18 MPa,and the constrained expansion proportion of XMCCC (21 d) is stable at around 0.028%.On this basis,combined with characterization methods,the formation mechanism and the gas sealing mechanism of XM-CCM were explored.The results show that the active functional groups such as hydroxyl group and carboxyl group in XG chelate with Ca2+on the surface of slurry particles,and the clay particles are bound between the hydration products of cement particles,which improve the mechanical properties of XM-CCC.The hexagonal plate Mg(OH)2 crystals generated by MgO hydration support the pores of the system,which improves the shrinkage resistance of XM-CCC.In terms of pore structure,XG changes the pore structure of XM-CCC and reduces the average pore diameter.When Mg(OH)2 crystal fills the pores,the crystal growth pressure generated can resist the pore pressure,keep the matrix from cracking,and reduce the porosity at the same time.Under the combined action of XG and MgO,the gas permeability coefficient of XM-CCC is only 1.47×10-12,which is much lower than that of surrounding rock.In economy of engineering application,XM-CCC has the advantages of convenient materials,simple production,low cost and simple and flexible construction technology.The field application results show that the XM-CCC coating is uniform,complete,and has good anti cracking and sealing properties,so it has a good application prospect.