We have calculated the ground and excited state energies and the orbital energies of three-electron atoms inside impenetrable spherical cavity. Energy eigenvalues and wavefunctions are calculated from the variational approximation method which is a combination of quantum genetic algorithm procedure and Hartree–Fock Roothaan method. In addition, the important parameters such as static and dynamic polarizability, oscillator strength and pressure have been investigated as perturbative. The results reveal that cavity radius and impurity charge have played an important role on the polarizability, the oscillator strength and pressure of the system. In addition, it is seen that when cavity radius is extremely large, all energies and the other physical parameters approach the values of a free space atom. As the dot radius decreases, the polarizability of system decreases due to the strong spatial confinement, but the pressure exerting on the system as the cavity radius R is shrunk increases. In addition, as the impurity charge increases, the oscillator strength decreases.