Based on the theory of elasticity and the Darcy's law，a simplified Well testing model for the dual cavity/fracture system in carbonate formations was established．Through Laplace Transformation and Inverse transformation，the expression of bottom pressure was Calculated．Then we analyzed the main factors affecting bottom pressure．The results show that Underground oil viscosity impact the pressure curve and the Length of line segment of Pressure derivative curve，Cave size Impact the pressure curve and the Concave margin of Concave section of Pressure derivative curve，Fracture permeability impact the Length of line segment of pressure curve．