Abstract: Microemulsion is a water-based environmentally-friendly pesticide formulation, and stability is its key quality indicator. The effects of inorganic salts, water quality and pH value on the physical stability of lambda-cyhalothrin microemulsion were studied by using the cloud point, emulsion stability, cold storage and thermal storage stability and surface tension of the microemulsion as the performance indexes, aiming to provide reference for the preparation and practical application of microemulsion. The results showed that with the increase in mass fractions of six inorganic salts (NaCl, KCl, CaCl₂, MgCl₂, KNO₃, and KI), the cloud point of lambda-cyhalothrin microemulsion gradually decreased. Among them, KCl caused the largest reduction in the cloud point, while KI resulted in the smallest decrease. Within a certain mass fraction range, the addition of inorganic salts had little effect on the appearance, emulsion stability, cold storage stability, and surface tension of lambda-cyhalothrin microemulsion. However, NaCl, KCl, and CaCl₂ had a certain effect on the thermal storage stability of the preparation. The water quality had a significant effect on the cloud point of the lambda-cyhalothrin microemulsion. The microemulsion prepared with deionized water exhibited the highest cloud point, which gradually decreased as the hardness of the water increased. However, water quality had no noticeable effect on the appearance, emulsion stability, cold storage and thermal storage stability, and surface tension of the preparation. The pH value had little effect on the physical stability of lambda-cyhalothrin microemulsion.