Chinese Acad Sci, Inst High Energy Phys, Beijing 100039, Peoples R China
; Chinese Acad Sci, Inst Theoret Phys, Beijing 100080, Peoples R China
; Sichuan Univ, Dept Phys, Chengdu 610064, Peoples R China
; Natl Lab Heavy Ion Accelerator, Ctr Theoret Nucl Phys, Lanzhou 730000, Peoples R China
; Tsing Hua Univ, Dept Phys, Beijing 100084, Peoples R China
Considering the finite volume of nucleons, a Lagrangian density is given. The first-order self-energy of the nucleon and the equation of state of nuclear matter are calculated in the framework of the relativistic mean-field approximation. Our results indicate that the effects of the volume of nucleons are not negligible.