The convergence property of multiframe blind deconvolution applied to improve the resolution of astronomical images is influenced by initial object estimate, constraint conditions and photon noise. A method of determining band limitation of the point-spread function from the optical imaging system parameters is proposed. The initial object estimate of blind deconvolution algorithm is formed by using Knox-Thompson method to reconstruct object phase from short-exposure images. A novel method, which is used to decrease photon noise, edge effects and ringing of restoration images is developed. An improved multiframe blind deconvolution algorithm with a strict constrained optimization method of the expectation-maximization based on maximum-likelihood estimation is presented. The restored images of the simulation data, and real Mars and solar-granulation data show that the proposed multiframe blind deconvolution algorithm is valid for overcoming effects of atmospheric turbulence and photon noise and improving the resolution of real observed astronomical images, and capabel of partly removing the diffraction effect of optical system on restored images.