You will need an active AV to HDMI converter.
Or get a new set top box with HDMI. If it's a cable box then your cable or sat provider will exchange boxes for you.
MERGED QUESTION Question from zkaligarh : "I have UC46+ projector there is no AV port and set top box have no hdmi so How i connect my set top box with projector?"
zkaligarh :
I have the UC46+ projector there is no AV port and set-top box have no HDMI so How I connect my set top box with a projector?
You will need an active AV to HDMI converter.
Or get a new set top box with HDMI. If it's a cable box then your cable or sat provider will exchange boxes for you.