MICROWAVE TUBE SIMULATOR SUITE (MTSS), tools for microwave tube design, is developed by Theory and Computer Simulation Lab. of University of Electronic Science and Technology of China. BEAM-WAVE INTERACTION SIMULATOR (BWIS), one module of MTSS, is a design tool for beam and wave interaction of microwave tube.BWIS simulates nonlinear interaction process between the RF microwave and the electron beam, and offers some information such as output power and phase of microwave. The three-dimensional (3D) nonlinear beam-wave interaction for helix traveling-wave tubes (TWTs) has been realized. Other microwave tubes' nonlinear beam-wave interactions are also planed to offer in the future, such as the coupled cavity traveling-wave tube (CCTWT) and the klystron.In the part of the helix TWTs' nonlinear beam-wave interaction, we developed a 3D relativistic beam-wave interaction model, which can describe the interaction process between the symmetric TM01 mode RF electromagnetic fields and the relativistic electron beam. This model can describe the 3D RF electromagnetic fields, the 3D motion of the macro-particles, and the 2D space-charge fields. Applying the Lorentz reciprocity theorem, the excited equation is obtained by the theory of waveguide excited. By Lorentz force equation and the conservation of energy, the 3D momentums and positions are obtained. The axial and radial ac space-charge fields are calculated by the harmonics wave means.In a linear beam device, the modulated electron beam can excite the backward radiation except for the forward radiation, which also interacts with the modulated electron beam. In this model, the backward radiation has been considered, and its effect on the interaction process has been analyzed. In the self-consistent equation system, the direct effect of the electron transverse motion on the energy exchange has also been considered. This model can also consider the finite focusing magnetic field, so the interception of electron by the wall can be analyzed.These figures (from figure 1 to figure 6) are the simulated results of a helix TWT, in which the parameters are the beam voltage V 0 =4500V, the beam current I 0 =450mA, the axial periodic focus magnetic field magnitude B 1 =1000GS, the signal frequency f=3GHz, the RF field phase velocity V p = 0.107c, where c is the velocity of light, the coupling impedance K c =30.142Ω, and the attenuation α= 4.825dB/m. The testing output power of the tube is about 360W. So the simulated results agree well with ones of the experiment.