In this paper, the surface plasmon resonance sensor, for measuring the absorptive sample’s real part of the refractive index, is studied via numerical simulations. Based on the Kretschmann optical arrangement, wavelength, angular, intensity, and phase interrogations are analyzed by using the Fresnel equation. The results show that, in comparison to the detection of transparent samples, the sensitivity of the wavelength interrogation, angle interrogation, and intensity interrogation improves, changes little, and decreases, respectively. For the absorptive sample, who has a complex refractive index’s imaginary part of 0.01, the sensitivity of wavelength interrogation enhances three times, whereas, that of intensity and phase interrogation reduce to 1/2 and 1/7, respectively. Fortunately, the degradation of the sensitivity, for phase interrogation, can be improved by changing the thickness of the gold film. In addition, the stronger the absorption is, the thinner the optimized thickness. By contrast, it can be found that the phase interrogation, with optimal thickness of gold film, has the highest resolution with the smallest linear measurement range. In order to balance resolution and linear measurement range, the angular interrogation is a better choice.