In this paper it has been proven that the fluid loss control of SMP primarily results from the improvement of mud-cake quality. The permeability K has been measured as an important factor of judging mud-cake quality.We have studied the changes oft heads or bed amount with temperature，salt content in the medium and PH value，as well as the relations between adsorbed amount and Water between loss of drilling fluid in the corresponding conditions. Particularly, the influence of the. NaCI content in the medium on the absorbed amount，the particle size distribution of clay in mud cake before and after SMP is mixed with SMC has been studied, hence a mutually relationship between these factors has been found.The mechanism of the anti-temperature and anti-salt properties of SMP lies in its quite strong thermal stability and hydrophilic power，as well as in its effective adsorption onto the surface of clay in the condition of high temperature and large salt content . when it is mixed with SMC or complexed with multivalent cations，such as Cr3+ thus, a stable protection for fine colloidal particles in such conditions is achieved
