This paper present a study on detection and evaluation method for monitoring joint of truss structure by measuring the impedance change of piezoelectric patches which were glued on the structure. The structure joint used in this study consists of two aluminium beams connected by bolts. The damage is simulated by dropout the bolts. The detection and evaluation method using bending vibration driven by single piezoelectric patch is proposed. In order to estimate the damage condition, the damage assessment index waveform change ratio r is used in this paper. Moreover, the effects of the weight and vibration act on the joint for damage detection and evaluation are investigated experimentally. Experimental results show the detection and evaluation method proposed in this work are validated for assessment of the dropout of bolts.