Abstract: The Results of one -dimensional effective melting heat, laser melting threshold intensity and metallography microscope analysis for the LY12 aluminium alloy targets irradiated by long-duration （6ms） 1.06μm laser beams are given in this report. A new explanation of yielding material damage by laser ablation combined with laser thermal stress is also presented. When laser intensity ranges from 24kW/cm² to 220kW/cm², the effective melting heat Q = 3.5 ⁵7kJ/g, and the laser threshold intensity for melting is about 10kW/cm².