I'm using ESP with USB to serial converter (D-SUN) is it possible to use the 3.3 volts of the USB instead of the Arduino Uno?
I don't know what that adapter is (a link would be nice, or at least the chip number it uses) but in general the 3.3v on a USB TTL adapter can only provide a small current. For instance the FT232RL can only provide up to 50mA at 3.3v. That may not be enough current to drive the RF circuitry of the ESP. The early Arduinos used the FT232RL chip for the USB interface and it was the 3.3v from that which was used for the 3.3v header on the Arduino. This was somewhat of a failing with those Arduinos since the 50mA limit was a real problem when people started using more 3.3v devices. That was one of the driving forces (as well as cost) in the decision to switch to an MCU for the USB interface.
So to be on the safe side I wouldn't use the 3.3v from the USB adapter to power the ESP. You are better using a 5v to 3.3v regulator circuit driven from the 5v of the USB. And yes, that could be a whole Arduino, or build your own on some stripboard.