Abstract: A method is developed to calculate the beam transverse emittance of theelectron linac. By means of deviding the beam into several concentric rings withequal amount of charges, their representative particle are traced in the injector.And with the obtained values of γ, P_γ and θ, some beam properties, such as theparticle motion traces, the phase convergence figures, the beam phase space, aswell as the beam RMS emittance at the exit of the injector can be calculateddirectly. The discussion about the effects of the cathod magnetic field and axialfield on the beam transverse emittance is also given in the paper.