TJ said
Thanks Mandrake. Not really understand the "recompose" part. I will try to take more picture tomorrow..

Well, when your center focal point is on the nearest eye, if you do not move the camera then
that eye will be in the center of the image.

It is usually best to "recompose" or... to move the camera, with your finger still halfway down on the shutter, so that the image will have a better composition.  This could well be by using the rule of thirds so that your model is not in the middle of the image.

By keeping your finger halfway down on the shutter you will maintain focus on the eye.

I hope I've explained it better.

TJ said
I just notice that I missed focus of her eyes in many other photos. Actually, how to accurately focus her eyes?I use matrix metering,should I change to spot metering?

My suggestion... Set the camera's focus mode to AF-S.
Select Single-point AF and choose only the center AF point.
Focus on the model's closest eye by holding the shutter half way down.
Keep the shutter half way down and move the camera to recompose the shot.
Press the shutter all the way down.

As you know the larger the aperture opening the less depth will be in focus.
Using 1.8f will give you a very narrow depth of field which will be in focus.
Try a larger aperture to give yourself a better chance of getting her eyes in focus.

Mandrake said
Portraits are never easy and you're off to a great start with these.
I like the variety of poses and the relaxed look of your model.
You might keep an eye on what's going on in the background.
That one duck on the left in the second photo bothers me a bit.

Thanks Mandrake. Actually, before I take the photo, the duck was standing next to each other & a distance away from her head. But I am too slow..haha

"Usually people will love the pictures, if they liked you and had a good time.  "

Thanks Oksana and Mandrake. This will be one of the most important thing in my portrait photography.

I just notice that I missed focus of her eyes in many other photos. Actually, how to accurately focus her eyes?I use matrix metering,should I change to spot metering?

#1 and #2 are my favorites. Good use of rule of third and lines in composition. I like that you have some blurry foreground in #1. It makes the viewer feel like he is picking into to her life without interfering. Agree with Mandrake about the bird in #2. It is very important to watch that nothing is growing out of model's head. 

#3 You missed focus in this one. I would prefer to have her eye in focus. I would also choose different crop. Ether closer and focusing on her eyes or give it a bit more space without cutting her hand at the joins. The same for #4. I kind of want more space at the bottom without cutting her fit off. Remember the rule of thumb: in most cases cropping at the joints is not a good idea. I would suggest to leave a bit more space then you need, so you have an option to modify your crop later on in post, if needed.