The present disclosure discloses a method for obtaining optimal variational parameters of a ground state wavefunction for a Hamiltonian system. The method includes initializing a plurality of variational parameters and sending the variational parameters to a quantum computing portion to output a plurality of measurement results. The method includes transmitting the measurement results to a classical computing portion to update the plurality of variational parameters based on the plurality of measurement results and an update rule, and determining whether a measured energy satisfies a convergence rule. When the measured energy does not satisfy the convergence rule, the method includes sending the plurality of updated variational parameters to the quantum computing portion for a next iteration; and when the measured energy satisfies the convergence rule, the method includes obtaining a plurality of optimal variational parameters for the Hamiltonian system.