The superlattices composed of polar/polar perovskites have two-dimensional electron gas (2DEG) at the interface, which has broad applications in nano devices, super sensitive sensor devices, high electron mobility transistor, etc. Tuning the electronic properties of the 2DEG at the interface perovskite superlattice, such as the coupling between strain gradient and the electronic properties of the 2DEG in correlated electronic systems, is of great significance. In this paper, the properties of (LaAlO₃)_4.5/(KNbO₃)_8.5 superlattice, which is composed of KNbO₃ and LaAlO₃, are systematically investigated through first-principles density functional theory calculations. The band structure of (LaAlO₃)_4.5/(KNbO₃)_8.5 superlattice exhibits 2DEG at the interface, which is consistent with the result in the literature. The band structure, density of states, magnetic moments and carrier concentration at the interface are fully investigated by using compressive gradient and tensile strain gradient, respectively. The results show that compressive strain gradient can effectively reduce the 2DEG concentration at the interface. When the compressive strain gradient coefficient reaches 12%, the 2DEG concentration decreases by 76.4%, and the interface magnetic moment disappears. The total magnetic moment of the superlattice decreases by 88.44%. When the tensile strain gradient is 12%, the electron gas concentration at the interface is increased by about 23.9%, and the interface magnetic moment is reduced by about 90.7%. At the same time, an obvious magnetic moment appears in the layer near the interface. Hence, the strain gradient can be a new approach to regulating the electron gas concentration at interface of perovskite superlattice. The tensile strain gradient increases the electron gas concentration at the interface, while the compressive strain gradient reduces the electron gas concentration. Therefore, it opens up a new way to exploring the regulation of high-performance spin polarized carrier gas at the oxide interface.