Can i ask how long can i use wire in mq2 sensor? What is the maximum length can be use? Both analogpin and digitalpin. Thanks 
It depends on what is connected to the wires. It can be metres to 100 metres.
Give more information on your usage.
Weedpharma
He said MQ2 gas sensor. ~165mA @ 5v, and analog output.
I use mq2 sensor. The pin that i use in arduino is digitalpin. How long can it takes?
Sorry, read it as a general how long question.
What distance are you wanting to run it over? This may be more useful than giving a max distance.
Weedpharma
I checking if how far can the wire extend, for some experiment in my mq2 sensor
Jinger:
Can i ask how long can i use wire in mq2 sensor? What is the maximum length can be use?
You can increase the length of the cable the same as you want to increase the inaccuracy of measurements.
The longer the cable ==> the more inaccurate the measurement.
There is no typical limit for inaccuracy you want to create with your hardware.
So decide how inaccurate you want your measurements to be, then use longer cables until you have achieved the inaccuracy that you want to have!
Perhaps cable lengths of less than 5 meters will work with acceptable inaccuracy.
Jinger:
I checking if how far can the wire extend, for some experiment in my mq2 sensor
There isn't a simple universal answer. The MQ sensor is arranged as a fairly high impedance (~10k ohm) voltage divider which makes for a low power signal susceptible to noise pick up in the cabling. How much noise pick up is a function of the environment in which your sensor is operating as well as how well the cabling is shielded. As a ballpark estimate, 10 meters is probably ok unless you have a particularly strong EMI environment. If I had to go hundreds of meters I'd consider digitizing the sensor data near the sensor and transmitting that more robust digital signal to my endpoint.