why is there no total vacuum condition on earth? I know that Bell jars are often used in laboratories to form and contain a vacuum but not total vacuum like space.So i don't understand why can't human make vacuum bell jar a total vacuum state?   
 A: Well, for one, space isn't a total vacuum. It has things in it! Particles do exist in space - they're just farther apart. So it's not a total vacuum. Though it's pretty close.  
I had to check wikipedia:

Ultra-high vacuum chambers, common in chemistry, physics, and
  engineering, operate below one trillionth (10−12) of atmospheric
  pressure (100 nPa), and can reach around 100 particles/cm3. Outer
  space is an even higher-quality vacuum, with the equivalent of just a
  few hydrogen atoms per cubic meter on average.

So, on earth we've been able to make vacuums almost as good as that of space. 
I guess the reason it's hard to make a vacuum on earth is because we have to fight against air pressure. You can have an open jar just floating in space and it's got a vacuum in it. 
That jar in the lab, however, when air particles are sucked out, creates an enormous pressure differential between the inside (no air) and outside (air). The bigger that pressure, the more we have to fight to get even one more molecule out. 
If we really wanted, I think humanity could create a better vacuum than space. But there's not really any good reason to do it - like CuriousOne said, the vacuums we have a sufficient for the experiments we want to do, and it would be very expensive. 
A: In a so-called low vacuum or partial vacuum, you basically have gas at low pressure:  Lots of molecules bouncing off one another, and sometimes bouncing off the chamber walls.  The gas is a fluid, and a mechanical pump can suck it out of the chamber.
In a high vacuum, it's different.  There are so few molecules inside the chamber that they act more like little bullets, flying in straight lines, ricocheting off the walls, and seldom interacting with one another.  At that stage, you aren't dealing with a fluid anymore.  Your goal is to get the individual molecules to find the exit hole and leave without letting any other molecules enter.  https://en.wikipedia.org/wiki/Turbomolecular_pump
When even that become ineffective, then the next strategy is to put something in the chamber that will immobilize any molecules that happen to hit it:  https://en.wikipedia.org/wiki/Ion_pump_%28physics%29 https://en.wikipedia.org/wiki/Getter https://en.wikipedia.org/wiki/Titanium_sublimation_pump
The ultimate problem though, is that no matter how effective your system for removing free molecules from the chamber, there will always be new ones that outgas from the chamber walls and from the sensors and other experimental apparatus that you put inside it.
You can reduce the outgassing from the walls very close to zero by using certain stainless steel alloys and highly polishing them, but the experimental apparatus is a whole 'nother story.  It has to be made of something, and you really can't do anything intersting inside the chamber without using materials that will outgass a little bit.
