Abstract: Flaky carbonate materials have become important thermoplastic polymer reinforced rigid inorganic fillers due to their advantages of non-toxicity, low cost and abundant raw materials. However, their preparation process is complex and difficult to achieve mass production. In this paper, combined with the problem of low added value of low-grade limestone in limestone industry, flaky Ca-Mg complex carbonates (FCM) were prepared by ultrasonic-assisted carbonization method using Mg-containing limestone as raw material. The effects of process parameters such as different Mg contents, different carbonization reaction temperatures and different ultrasonic powers on the morphology of the product were investigated. On this basis, the active FCM and poly(butylene adipate-co-terephthalate) (PBAT) resin were blended and extruded into composites. The effects of different kinds of fillers and different ratios on the properties of composites were compared. The results show that Mg content, ultrasonic power and reaction temperature have a significant effect on the morphology of Ca-Mg composite carbonate. With the increase of Mg content to 20.61wt%, reaction temperature to 70℃ and ultrasonic power to 400 W, Ca-Mg composite carbonate products with a large number of flake structures and a specific surface area of 23.5 m²/g are obtained. The composites with active FCM showed excellent mechanical properties. When the content of active FCM was 20wt%, the impact strength, flexural strength and flexural modulus of the composites were 1 time, 2 times and 2.8 times higher than those of pure PBAT, respectively. When the addition amount is 40wt%, these performance indexes are further improved, which are 1.2 times, 2.6 times and 4.8 times higher than that of pure PBAT, respectively. More importantly, the soil degradation rate of the composite material added with the active FCM is significantly improved, which will effectively promote the degradation of the composite material after use, so that it can quickly integrate into the natural environment after completing the service mission, further reflecting its environmental protection and sustainable characteristics.