I would like to download mac os x 10.5.9, who can provide? Thank you！

Assuming the 10.5.9 was a typo (or brain hiccup) here's the apple downloads page for 10.5.8 related software. The combo and incrimental updates (i.e., you already need the OS to update) are there. If you did really mean 10.5.9 don't bother putting that in the search on the apple download page I linked to because you won't find anything.

So we know more about it...

At the Apple Icon at top left>About this Mac, report the OSX version listed there, then click on More Info, then click on Hardware> and report this upto but not including the Serial#...

Hardware Overview:

Model Name: eMac

Model Identifier: PowerMac6,4

Processor Name: PowerPC G4 (1.2)

Processor Speed: 1.42 GHz

Number Of CPUs: 1

L2 Cache (per CPU): 512 KB

Memory: 2 GB

Bus Speed: 167 MHz

Boot ROM Version: 4.9.2f1

There is no OS X version 10.5.9.

OS X 10.5.8 is not available to download, you have to buy the boxed disk. The going price is about $300. Try eBay.

If you can get your work done with 10.6 (Intel only) that cost is only US$30, and the Apple Store online will ship it to you. It does not support AppleTalk Printing, if that matters to you.