Which other site are you talking about and it is hard to comment on your portfolio without a link.

Give it time though, if you only have about 5 views/image it is pretty hard to draw much of a conclusion from that.  The sample size is much to small.  iStock is generally the best return per image for most people.

Is my photo not suitable for IS style?

You know what would help?  Seeing the photo.

Uploading some photo to IS just several weeks ago.The acceptable ratio is about 60% and views are about 8-9 per photo but no download.  

At the same time,I found the sales/view in other agency is about 5.It means every 5 customers view on my photo will generate one download.Is my photo not suitable for IS style?

IMHO if IS approved it, it has something for sure, upload a few more

My top three non Vetta sellers average 30:1
Less popular files have a much higher view/sales ratio.

ETA: I have one Vetta file that has a 1351:0 ratio

I have had quick sales sometimes from fairly new images.  But I must say that these are nearly always rather unique images, of stuff that however non-commercial it may appear, they don't have a lot of competition from existing images.  Other images, unique or otherwise, seem to be comatose for a few months and then mysteriously start getting regular sales.

As for the OP's question, getting 10, 50 or 100 views with no sales is pretty common, at least for me.  If you just keep shooting and uploading, you may be very surprised at which images really take off (eventually) and which ones get hundreds of views with no sales.

I suggest you to spend more time shooting and learning photography and less time doing maths. Very often number of views, acceptance  ratio and other statistics are not important, as long as you make sales.