Cooling efficiency in electron cooling systems is closely related to the velocity of electron. The velocity of electron has offset due to the space charge of the intense electron beam in the drift tube of the cooling section and thus increases the temperature of electrons. In order to minimize this effect, a new type of electron gun is adopted to produce a hollow electron beam in HIRFL-CSR e-cooler project. The hot ion beam is cooled by Coulomb interaction with intense and cold hollow electron beams. Using typical parameters of the CSRm e-cooler, theoretical calculations comparing the impact of the space charge field on electron velocity for solid and hollow electron beam are carried out. (C) 2003 Elsevier B.V. All rights reserved.