In this article, the X ray special line radiation from Z-pinch Al plasma is calculated by using non-local-thermodynamic-equilibrium model (NLTE) based on digital energy level. The electron density of Z-pinch plasma at centre is obtained. The single plasma state parameter cannot well describe the special line radiation. In the next step, the Z-pinch plasma is divided into two parts: high electron temperature plasma at centre and low electron temperature plasma. The superposition of radiations from two parts is analyzed, and modified calculation result is presented. The calculation results are significantly improved after the superposition of radiations from two parts has been taken into account.