During the interaction of ultra-short and ultra-intense laser pulse with plasmas, high energy electrons will be produced near to critical-density surface. When the hot electrons knocked out inner-shell electrons of the cold material, K α characteristic lines emission will be created. 超短超强激光与等离子体相互作用过程中,在临界密度面附近产生能量很高的超热电子,当其能量超过靶后冷物质K壳层的电离能时,就会激发冷物质的Kα特征线。