I want to remove catalog price rule when customer apply discount coupon in cart page.
Because i want to give one discount at a time and when customer is going to apply discount code i need to remove catalog price rule from cart items.
The short answer is that you cannot.
When you create a catalog price rule it doesn't take effect until you apply the rule. So, likewise, when you unset a catalog rule, you need to unapply the rule, at which point other customers will also get the higher price.
As a workaround, you can create an observer that will fire when your coupon gets applied and in the observer method set the price of the item in the quote to what it would be without the catalog rule.