Abstract: Aone-dimensional, two-stream analytical code has been developed to study the sheath structure formed by electron beam continuously injected into vacuum. Injected electrons will be decelerated and then drawn back to the surface of the spacecraft by the positive charges due to the electron beam injection into the vacuum from the spacecraft. The injection beam and return beam form two electron streams with the same density and velocity distribution in the sheath. The stagnetion point is at x=v_o/(3ω_o)(where v_o is the initial velocity of beam injection, ω_o is the plasmafrequancy of incipient injected electrons). Also, electric field distribution and electron density distribution in the sheath are given out in this paper.