I have problem when it comes to smash the shuttle!!When i smash the shuttle..it always hit the net!!!Can any1 help me!
Ask somebody to check your forehand stroke technique. If the shuttle constantly keeps going into the net, it's likely that you are not raising your left-hand or your non-racquet arm up to stabilize your movement. Remember, racquet up. Keep practising until you get it right. It's also possible that you are hitting the shuttle from a low position. If you can provide us with a video of you playing, it would be more helpful as we can give you more advices.
Regardless of other technique issues, you should be able to hit the shuttle over the net. Give yourself a larger margin for error.
Chances are if you are hitting into the net consistently that your technique and point of contact are probably not correct. As well, you may mentally be trying to hit the shuttle "hard". I have found trying to smash "hard" often leads you move your point of contact to a point where you end up smashing into the net. As jhirata has said, you would probably get a better breakdown if you have a skilled player/coach break down your smash in person or provide the more knowledgeable people here with a video.
Trying to hit hard makes you swing with very bad technique and for a lot of people actually introduces really bad swing mechanics. Just relax and focus on your technique to get a consistent smash that goes over the net. The strength of your smash is almost entirely tied to refining your technique. Just work on getting the correct motion and contact point and the power will just flow from it. If you watch some of the training videos that people have made available elsewhere on the forums it may help. My biggest suggestion about smashing... Power is not everything. We as beginners learning the sport of badminton almost always gravitate to the belief that hitting it hard = I win. In fact accuracy of placement is significantly more important imho. On my good days when my technique, timing and mindset are all in sync(not may unfortunately), my smash will be placed well. Of course the speed of my smash has not changed but my opponents who can't return think it is faster then normal.
I actually had this same smashing problem for ages until like.. December last year. What I did to improve my smashing is that I practised doing alot of drops. I'm assuming that you're still a beginner. Take turns with another person to drop/lift. Drops are basicly like slow, but precise smashes. Once you get the hang of it, try half-smashing. Half-smashes are like fast drops but rather slow smashes. It uses alot of wrist power. And if you get the hang of that.. You probably won't have much problems with your smashes. Here's a video of Sir DinkALot practising half-smashes and drops.. http://www.youtube.com/watch?v=lDOui08KA2g This is actually a good drill to improve your precision.