The niches of the dominant species of spiders and their target pests including rice plant hoppers and leafhoppers were studied. The results indicated that the increase or decrease in the value of niche breadth of spiders followed those of the pests. It was showed that there was a close relationship between the spiders and their preys. The indices of niche breadth and niche overlap of spiders in the late rice fields were larger than those of the spiders in the early rice fields. A phenomenon of alternation was found in the indices of niche breadth and niche overlap among the spiders in the different development periods of rice. An explanation to alterative phenomenon and followed phenomenon was discussed in the paper as well.