Focusing an Nd∶YAGpulsed laser beam onto surface of an aluminum(Al) target ,ablating it ,Al plasma would be induced upon the surface. Protected with Ar in the process ,it would induce atom Ar breakdown ,and farther more ,a lot of Ar+ ionic characteristic radiations appeared accompanying the A l plasma ’s emitting. Based on the Ar + ionic characteristic radi-ations ,we studied time2resolved behavior of three Ar+ ionic characteristic lines ,Ar Ⅱ385. 06nm ,Ar Ⅱ386. 85nm and Ar Ⅱ404. 29nm ,respectively. Electron temperature of the plasma in the stage of ionic emission was approximately calculated. Electron number density of the plasma in the stage of Al characteristic radiation was estimated. The results show that , in the stage of ionic emission ,the electron temperature of the plasma ranged from 1. 2 to 1. 9eV ,and decreased successively with delayed time increasing. In the stage of Al characteristic radiation ,electron number density of the plasma was about 2×1018cm- 3 .