I am having a flysky ct6B reciver and I want it add a camera to my quadcopter but I can't figure from where to get 3.7 v so I directly added dc input from revicer to the camera device.
It is working and recording but I wanna know that will my receiver fry with this use? 

Isn't there any skilled person in this forum??

Yes receiver will / may fry the camera. So do not connect till below are clear.....
1. Rx is getting power from ?
2. what is the input voltage range of your camera
3. For quad which battery you are using

regds
Saurabh

1 From Esc wire
2 3.7v
3 11.1v Lipo

Ok ...
So you are not using Opto ESCs.
> now in your case the RX is getting 5 Volts from ESC.
>If your camera was capable of 5V you could have connected it to RX. ( center pin is +ve, other 2 are GND and Signal)

you cannot connect the camera to RX.

Still if you want to connect ... buy a 3.3Volt regulator  and take voltage from RX.

https://www.amazon.in/MAKER-HACKER-AMS1117-LM1117-ADJ-Regulator/dp/B073ZF1HCY/ref=sr_1_fkmr3_1?ie=UTF8&qid=1507627481&sr=8-1-fkmr3&keywords=3.3+volt+regulator+ic


hope this clarifies.

BTW which camera is this Xiaomi??

regds
Saurabh