In order to analyze the surface-enhanced Raman scattering (SERS) electromagnetic enhancement properties of Ag nanoparticles (AgNPs)/carbon nanotubes (CNTs) composite structure, we establish the AgNPs/CNTs simulation model by FDTD Solutions software and simulate the electric field distribution of AgNPs/CNTs by changing the size of silver nanoparticles, the gap between two AgNPs, and the excitation wavelength. The simulation results show that there are two kinds of “hot spots” for AgNPs/CNTs composite structure, one existing between CNTs and AgNPs, and the other existing between two AgNPs on CNTs surface. It is found that, with the increase of AgNPs size, the maximum electric field intensity first increases and then decreases; with the increase of the gap between two AgNPs, the intensity of the electric field decreases; when the excitation wavelength is 532 nm, the electric field intensity around AgNPs/CNTs is the strongest. It is concluded that, taking the SiO2 film as the base material, when the size of AgNPs is 60 nm, the gap is 2 nm, and the excitation wavelength is 532 nm, the electric field intensity is the strongest and the calculated enhancement factor is about 10 8. The theory and experiments show that SERS enhancement effect of the Ag film is better than that of the SiO2 film.