Experimental study of aluminum wire array Z-pinch was conducted on Qiangguang-I facility （1.5 MA, 80 ns） to produce —1.7 keV characteristic X-ray radiation. With fixed wire diameter of 20 μm and annular diameter of 12 mm, K-shell yield up to 0.9 kJ/cm and 1.1 kJ/cm was obtained for wire number N=8 and N=12 arrays, respectively, which are much higher than that for N=16 and N=24 loads. X-ray power waveforms and time-resolved images showed that several implosions occurred due to the existence of trailing mass. During 60%—80% of the whole implosion time，the wire array almost stayed at its initial position rather than running inwards. Main implosion was completed in the next 25—30 ns, with parts of load mass left behind and forming so-called trailing mass. At later time of main implosion, load current was transferred to trailing mass left in outer radii, and caused secondary even tertiary implosion, which also contributed to total K-shell yield. Appearance of trailing mass might be caused by azimuthally correlated axial modulation, consisting of hot spots and gaps on wire plasma column, as well as the development of other inhomogeneities.