The notion of n-width, introduced by Kolmogorov, has received considerable attention in recent years within approximation theory. Pinkus calculated n-widths on complex plane in 1986. In this paper we will be concerned with n-widths in Hardy space. Using the Poissoon integral operator, we derive the optimal basis. And we can see the space, generated by eigenfunctions of the Poisson integral operator, is a optimal subspace.