TestLink

I have product A,B,C...above ten.
and every product has about 40 test suites.
Those suites between product only have few difference.
if i create all product in testlink,when i want to change a testcase,i need change every product.
if i only create one product in testlink,I want to get these easliy:
1 this case does fit for some product ?
2 this case is execute on which product ?
3 above statistics
How can i do it ?

Use export/import.

So we set up a master project with all test cases tagged with keywords. Then for a new product, we just search for test cases in the master project, and like havlatm, export the ones that apply to the next product and import them into the new product's project.

We made the test cases generic enough that environment variables could be set up in the new project that wouldn't effect the test case specifically. This won't work if you're doing purely scripted testing where your testers rely on specific steps to accomplish the task.

I don't understand you last sentence. One thing is Test Specification and different is your set of scripts. Both are independent and meet for case that a Test result is stored within a Test Plan.
You can have one large Test Project and particular work will be defined via Test Plans (no need to export/import).

You can also deliver test results via TestLink API. Your script should be configurable enough to easily modify target project/test_plan.

thank you.
1 export/import.
i have already creat products and testcase, my problem is how to modify a testcase(i need to modify all product .This is boring and wasting my life). if use export/import,other product will have 2 times testcase, and if i delete old testsuite,all test results will gone too.

2 key word
If only a product:
I want to know does a testcase fit for a paticular product.
I want to search all testcase with a key word .
I need to record test results on paticular product or some products.
can key word do these?

I made the test cases generic enough that environment variables could be set up in the new project that wouldn't effect the test case specifically. This won't work if you're doing purely scripted testing where your testers rely on specific steps to accomplish the task.