The self diffusion coefficients D of lithium ions in PAN-EC/PC-LiClO4 gel polymer electrolytes with different compositions and at different temperatures have been directly measured by field gradient NMR spin echo technique. The results indicated that self diffusion coefficients D of lithium ions were dependent on the mass ratio x% of lithium salt, and had a maxiumum at x=10 in the range of x=5 to 20. It was suggested that this was probably involved with transport mechanisms of the hopping of lithium ions, and with two kinds of interactions: the interaction between Li+ ions and plasticizer EC, and the interaction between Li+ ions and network polymer PAN.