Through the calculation of plasma with electron density of 1×1019 cm-3, and cooled only by electron thermal conduction, we got the plasma parameters varied with time and space. Under this contition, we calculated the gains of 5f-3d and 4f-3d of Li-like Al ions using C-R model. It is shown that once there are suitable initial plasma conditions, the soft-X-ray gains can be produced in plasma cooled only by thermal conduction.