The invention relates to a surface plasma resonance (SPR) phase measuring device for measuring the thickness of a nanometer metal film. The SPR phase measuring device comprises a laser, a collimation lens, a first polarizer, a prism-type SPR sensor, a plane reflector, an interference system, a second polarizer, a couple charged device (CCD) camera and a computer 10, wherein the laser, the collimation lens and the first polarizer stay on the same optical axis, and the second polarizer and the CCD camera are placed on the same optical axis; the laser emitted by the laser enters the prism-type SPR sensor after passing through the collimation lens and the first polarizer, after being reflected through the plane reflector to the interference system, the reflection light passes through the second polarizer, an interference image is received by the CCD camera, and then the obtained interference image is recorded by the computer. The SPR phase measuring device has the beneficial effects that the structure is simple, convenience in operation can be realized, the error caused by a light path is inhibited by adopting a laser interference-based SPR phase modulation method and adopting the same light path to measure a coating area and a non-coating area of the prism-type SPR sensor in the measuring process, and high measurement precision can be realized.