how to import cck data from drupal6 to drupal7?
You could use the Migrate module along with the Drupal-to-Drupal data migration module

Migrate


  The migrate module provides a flexible framework for migrating content
  into Drupal from other sources (e.g., when converting a web site from
  another CMS to Drupal). Out-of-the-box, support for creating core
  Drupal objects such as nodes, users, files, terms, and comments are
  included - it can easily be extended for migrating other kinds of
  content. Content is imported and rolled back using a bundled web
  interface (Migrate UI module) or included Drush commands (strongly
  recommended).


Drupal-to-Drupal data migration


  migrate_d2d provides a framework based on the Migrate API for
  migrating content from Drupal 5, Drupal 6, or Drupal 7 sites into the
  Drupal 7


Another option would to use the feeds API to import data. You could create feeds of the contents in drupal 6 and use feeds API to create the required contents in Drupal 7

Data export import is another module that does import and export of content.

Node export this another module that can be used along with Feeds