I have tried to apply Catalog Rule on product but this discount rule is not applied which product have already special price and tier price.
so is this default magento behaviour of its bug or any solution for that ?
Magento applies catalog price rule on the product price that we set in the admin in price attribute.
On frontend, Magento shows the minimum price.
Suppose product price is 25 and catalog price rule is set to give 10% discount which means the product price will be 22.5
Also, there is special price set to 20.
Now the minimum of the above is 20.
So, the product final price will be 20, which will be shown on the frontend.