@Nagendra-yedem you should always include details of what device you have and what firmware verson you are using.
i assume you are using Python, but you didn't mention what version so this would determine how you would install smbus.
First you need to edit /etc/opkg/distfeeds.conf, uncomment line 5. Now run:
If you are using python 2.7 you run the command:
opkg install python-smbus
If you are using python 3 you run the command:
opkg install python3-smbus