How to setup year increment? I use Date module in D7, and I create new field "decade" (field type is Date). 

Also in the settings, I add a custom input format 'Y' (only years). There is increment for time (+/-30 minutes), but I need increments for years (+/- 10 year). In node add form I need selectbox with values like:

1700
1710
1720
1730
....
now
How can I do that?
You shouldn't use a date format for your field

I advice you to use CCK module (7.x-2.x-dev) 


  some miscellaneous helpers to do things that core will not do, like
  maintain the PHP code snippets some fields may have been using to
  define allowed values (partially working)


With this module, you define these kind of allowed values from a php code