Embodiments of the present application relate to a solid electrolyte and a preparation method thereof, and an electrochemical device and an electronic device comprising the same. The solid electrolyte of the present application includes a solid electrolyte material being represented by the chemical formula of Li1+2x−2yMyGa2+xP1−xS6, where M is selected from the group consisting of Sr, Ba, Zn, Cd and a combination thereof, 0≤x≤0.2 and 0≤y≤0.05. Embodiments of the present application provides a solid electrolyte having good stability with lithium and ionic conductivity by forming the solid electrolyte using lower cost solid electrolyte materials and optimizing the material composition and a crystal structure thereof. At the same time, this also reduces the manufacturing costs of the solid electrolyte, and improves the structural stability of the solid electrolyte.