We presented a comparison of magnetic properties of ［Cot/Fe3t］5 (t=2, 3, 4, 5nm) multilayers prepared by DC magnetron sputtering on glass and Si substrates. For the multilayers with the same t but prepared on different substrates, it was found that the saturated magnetization differed little, but the coercivity differed greatly. Moreover, the difference in coercivity mechanism was analyzed theoretically to explain this difference.