A method is provided. The method includes: determining m first parameterized quantum circuits and a second parameterized quantum circuit of an m-dimensional quantum system; obtaining m first quantum states obtained after the first parameterized quantum circuits act on an initial quantum state and m second quantum states obtained after the quantum channel acts on the m first quantum states; obtaining a quantum state matrix obtained after the second parameterized quantum circuit acts on the initial quantum state, where diagonal elements of the matrix correspond to the first quantum states to constitute an ensemble; optimizing parameters of the parameterized quantum circuits by minimizing a loss function, where the loss function is determined based on Holevo information of the quantum channel at the current ensemble; and determining the Holevo information, obtained after the optimization, of the quantum channel as an estimated value of the classical capacity of the quantum channel.