I mean,the bolter seem heavy,and seem like it's the power armor make the Space Marine can use it(strength improved).

So,can a human without power armor use bolter?

I can't cite my source, but I've heard multiple people reference a story where a guardsman tried to use a bolter and the recoil either ripped his arms off or severely damaged them.

http://wh40k.lexicanum.com/wiki/Boltgun

and apparantly that quote is from
http://wh40k.lexicanum.com/wiki/Dark_Heresy:_The_Inquisitor's_Handbook

Yes. It depends on the pattern though, as already explained, most will destroy a normal human if not modified for their use.

"Some models are designed specifically for normal humans which include smaller grips and lighter construction, though these variations are rarely as finely fashioned as Space Marine weapons. Many such weapons are ancient heirlooms and relics passed down through a family's generations. Cheap bolt weapon models can be found on black markets and backwater planets, but will often breakdown quickly because of the specialized nature of their ammunition." [source]

Every TT model in the IG army with access to the ranged armory section (Sergeants, Platoon Leaders, Commisar', and HQ's) can select a boltgun, so they're actually quite common.

If nothing else, look at this beast of a man. There's your answer.

So yeah, not an Astartes pattern boltgun with its ungodly recoil, but they do make boltguns specially designed for human operators.

Well, maybe a Catachan can...

Yep they can use it

Once

Read all this and ask myself: "Why on Earth the normal human shouldn't be able to use the bolter?". AFAIU from the (technical) descriptions - the closest modern real-life analogues to the WH 40000 bolter are:

Neopup PAW - 20:



And XM-25:



Both fired by normal humans pretty well (having the stock, however, absent on the Astartes model bolter. Without stock, from the hands, both these would fire with "plus-minus bus stop" accuracy). The latter even sounds fairly close to the Munitorium or Ultramarines movie bolter, BTW )

Heavy bolter - yes, it's to unwieldy for ordinary human thus is fired from the tripod. Yet again, the closest RL analogue to the HB is - XM-307:



Weapon of such a format wouldn't be a burden for the 700-pound Space Marine in power armor, however.

all these project cancelled or paused

Pretty much like Ramjet and Gyrojet weapon systems (seeming to be an RL base principles for building the bolt weapons). But damn - it's only 3rd Millenium, not 41st.

I remember what my father said,why in 41 st human still use real people to fight lol.