I downloaded custom contents such as clothing, hair, and objects. The game somehow crashes and I have no idea why. The CCs seems to be fine for me.

Any help is appreciated

Does it crash if you load different households? Different neighborhoods? Does is crash as soon as you try to enter a household, or can you play some? Do the crashes have anything in common?

And of course: Does the game still crash if you take out the entire Download folder?

1. Yes
2. Yes
3. It crash
4. CC
5. yes, it works perfectly.

That's your answer- either your game cannot cope with the amount of CC you have, or else you have some CC which is causing the game to crash.

Game Help:Finding Problem Custom Content^wiki

You have a piece of bad CC. If the crashing only just started and you know what you recently downloaded try pulling it.
If you have no idea what it could be you will need to do a 50/50 hunt.

Adding CC --> crashing = item the game disagrees with.
I've had both furniture and clothes that crashed the game, so nothing is a 100% "safe" item.

Make sure to read about the items you download whenever there's info attached, make sure the items agree with your configuration of EPs/SPs (for instance, don't try using items for AL/M&G if you don't have those packs - especially lots and mods), make sure mods are compatible with your EPs and other mods you're using (don't add too many mods/hacks in one dump, or they're a nightmare to diagnose), and don't add large CC dumps in one go. Test with smaller amounts, and preferably check if all the items work/show up/don't create immediate issues before adding new items. Otherwise you'll be stuck doing 50/50 with a large amount of random items and no idea where to start.

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Also (if you haven't tried it already) delete the cache files. They can mess around with CC, especially in the case of larger CC dumps, mods, etc., and can occasionally cause the game to either not start or to crash. Some people need to delete these files often.

"Accessory.cache" and "Groups.cache" for issues with TS2 or Bodyshop. "ContentRegistry" if you've used Bodyshop, and "Cigen.package" if you need to refresh Bodyshop thumbnails. They're all found where the saved game is (not install location), usually in the "...Documents\EA Games\The Sims™ 2 Ultimate Collection" or "...Documents\EA Games\The Sims 2" folder, depending on game version.

There are a few other ways to handle some of the files (using an empty file, or startup alternatives like the RPC that auto-deletes them), but just deleting them is fine, too.