The invention relates to a device and method for detecting the grout compactness of splice sleeve, the device comprising a preloading member, a force transmission rod, a telescopic adjustment member, a vibration sensor and a data acquisition system. The rigid preloading member is used to fix the force transmission rod to the wall where the connecting structure of the splice sleeve is located, so that the end of the force transmission rod can be securely fastened to a rebar surface of a splice sleeve to be detected; the vibration sensor is fixed to the force transmission rod; the data acquisition system is used to acquire vibration signals from the vibration sensor. The grout compactness of splice sleeve is quantitatively analyzed, and a time-domain and frequency-domain signal may be used to obtain a peak-to-width ratio RNpw and a peak frequency ΩPeak signal to serve as a standard for the quantitative analysis.