An apparatus for detecting surface plasmon resonance (SPR) comprises a light source, a light-coupling unit, a phase-resolving module, and a data-processing unit. The light source provides a light beam emitting into a surface of a metal film to generate surface plasmon resonance. The phase-resolving module is configured to split the reflection light of the light beam on the surface of the metal film into a first light, a second light, a third light, and a fourth light, and to detect the intensities of the lights simultaneously. The phases of the first light and second light differentiate by 90 degrees, and the phases of the third light and fourth light differentiate by 90 degrees. The data-processing unit calculates the phase variation of the surface plasmon resonance on the metal film based on the intensities of the first light, second light, third light, and fourth light.