Can I clean range hood exhaust duct without reaching it?
Exhaust duct is greasy clogged, right?  - We do not know, we can not see it from here. 

How can I clean it, but not access it? - You can not. You have to access the duct if you want to clean it. 

Are there safe chemicals I can spray at range hood fans? - There are dozens of safe grease cutting/cleaning chemicals on the market. 

Then when I turn on range hood fans, these chemicals suck into exhaust duct, destroy all grease, and everything sucked out? - NO, that is not how it works. There is no sucking mechanism in your duct. 

I don't want remove range hood or open exhaust duct. - Sorry but removal of the hood is required to clean the duct ( and to even assess if it is indeed full of grease.)

Here is the USA distributors web site. Your model is the R-727II. 

Here is the contact email for sakura USA -  achoo@sakura-usa.com

Here is  link to  a search results on YouTube for cleaning range hoods.  

Your unit does appear to be rather unconventional, looking at the photo it is not clear where the filters are or how to access them.

That is why you need to contact them directly. 

UPDATE: Your range hood does not have "traditional" screens that trap the grease. There are two clear plastic grease collectors for each fan. one is mounted to the cone shaped fan guard and the other is at the back of the unit behind each fan near the wall. I believe the premise is condenses or collects on some unknown to me part of the unit and then drips down into the removable plastic receptacles. In theory the grease should not be getting into your duct. this video, not in English shows a brief simulation of the grease trap at work near the end of the video. Here is link to a parts page that has the plastic trays. 

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