In the surface plasmon resonance (SPR) sensor system with Kretschmann configuration based on wavelength modulation technology, the theoretical model of the influence of beam reshaped system and the beam diameter on the convergence angle is built. The influence of convergence angle of probe beam on resonance wavelength, the full width at half maximum (FWHM) and the depth of resonance peak is analyzed. As the convergence angle decreases, the resonance wavelength is enhanced, the FWHM is reduced, and the depth of resonance peak is enhanced. As a result, the capacity of resisting disturbance is enhanced, and the system resolution is enhanced. It is confirmed by experiment, and the experimental result fit well with the simulated one when considering the influence of convergence angle. When the convergence angle varies from 0.8° to 0°, the resonance wavelength varies from 662 nm to 623 nm, the FWHM is reduced from 157 nm to 117 nm, and the depth of resonance peak is enhanced from 70.5% to 93.3%.