这个是ai帮助文件里面找到的：
To create a pattern:
1、Create artwork for the pattern following Guidelines for constructing patterns.
2、To make the pattern less complex so that it prints more rapidly, remove any unnecessary detail from the pattern artwork, and group objects that are painted with the same color so that they are adjacent in the stacking order.
3、Optionally, to control the spacing between pattern elements or to clip out portions of the pattern, draw a pattern bounding box (an unfilled rectangle) around the artwork you want to use as a pattern. Choose Object > Arrange > Send to Back to make the rectangle the backmost object. To use the rectangle as a bounding box for a brush or fill pattern, fill and stroke it with None.
4、Use the selection tool to select the artwork and bounding box (if any) that will make up the pattern tile.
5、Do one of the following:
Choose Edit > Define Pattern, and enter a name in the New Swatch dialog box.
Choose Window > Swatches (if necessary), and then drag the artwork to the Swatches palette.
