I am working which with sensors on raspberry pi.I am able to connect the all digital sensors with raspbeery pi.How to start with analog sensors.Should i require a Analog to Digital converter IC?
Yes, you will need an ADC, the Pi has no analogue inputs or outputs.
A popular choice would be an MCP300X (10 bit resolution where X is the number of channels) or MCP320X (12 bit resolution). They connect via the Pi's SPI bus (GPIO 7-11)
You will find plenty of software and tutorials for those chips and the Raspberry Pi.