Hello, I want to understand how this high voltage tester work? what kind of bulb neon used here?

 

This is a voltage divider. It doesn't divide equally the HV applied, so you need to add a different value resistor to the leg of each neon bulb.

Neon bulbs usually rated at 90VAC. The last one needs a bigger resistor than the previous one. (after crude calculations)

You need to make accurate calculations

 

Hmm, at 6kV I calculate power loss in the first two resistors about 450W. That seems a little bit excessive

 

With my calculations, it appears that the two first resistors should be 122W. Much higher than the 1W showed at the schematic.

 

Do you have the links of circuit?

Are you trying to build this measurement tool to measures the high voltage generator that you built used the ne555?

 

Do you have the links of circuit?

Are you trying to build this measurement tool to measures the high voltage generator that you built used the ne555?

Yes I built a high voltage generator (electrical fence) but unfortantly didn't work well

 

They probably get away with it as the electric fence just pulses once every few seconds so the power is minimal.
Definitely DO NOT try to use this on 6KV AC or DC!!!!

 

Yes I built a high voltage generator (electrical fence) but unfortantly didn't work well

According to the datasheet of neon, if you build it with that circuit, all the neons may damaged first, because the voltage crossed on the neon are too high, so it needs more clear info to make sure that the input voltage to calculates the draw current.
Neon Indicator Lamps.

You still didn't provide the links of circuit where does it came from?

Are you trying to build this circuit?

To build this kind of circuit needs more acknowledge and skills, otherwise it may hurt yourself and if the information still not enough then this thread could be locked for the safety reason.