I need help in my project fire fighter robot i used flame sensor to detect the fire but sensor sense the intensity of light of sun and it become blind and no sense the fire

 

Sounds more like a school project than repair. Probably nothing wrong with your sensor; albeit, you haven't given any information about what it is and how it works.

How about some basics? Where are you trying to detect fires? In a furnace? At the beach? In a forest? Etc. What sensor are you using? Where are you /your robot located relative to the fire?

 

First thing that comes to mind is to use two sensors, one for visible light and the other for infra-red.
Determine the ratio of IR : visible.

 

I might try to detect the variations in the output of the fire in contrast to the relatively steady output from the sun.

 

I would use a pyrometer chip, such as this one.