Magento 2 is based on a better code that makes Magento 2 easier and flexible to use. Besides, It also supports efficient APIs, theming capabilities, and turnkey extensions. As you are probably aware of, Magento 2 will come with a brand new architecture and database design. To ease up upgrade process, Magento released official Data Migration Tool that will help developers migrate store data from Magento 1 to Magento 2.

Data Migration Tool transfers data from M1 database to M2 database based on set of rules defined in xml files. To be clear, this tool only transfers data. Themes and customizations of your store can’t be automatically changed or migrated to Magento2. Migration tool migrate can migrate all-settings, products, categories, orders, customers, product review and linked-product relation(cross sell, related products) etc. Basically it migrate everything. If you have multiple store, It can migrate all stores and linked data with all stores. You can delete/filter migrated data on Magento2 store.

It is highly recommended to create a backup of the Magento 1 database and to truncate all the log tables before upgrading the website.

Official Magento data migration guide url: http://devdocs.magento.com/guides/v2.2/migration/migration-tool-install.html

Please follow below Steps for Data Migration:

1. First change/increase php memory limit, max execution time, max input vars, max input time2. Hit composer update command to update all the local repo3. Run below command to install migration toolcomposer config repositories.data-migration-tool git https://github.com/magento/data-migration-toolcomposer require magento/data-migration-tool:<M2 version>(composer config repositories.magento composer https://repo.magento.comcomposer require magento/data-migration-tool:2.3.2)4. Go to your vendor/magento/data-migration-tool/etc/opensource-to-opensource/<magento 1 version folder>5. rename config.xml and map.xml [remove dist]6. Change source and destination DB in config.xml<source><database host="localhost" name="m1databasename" user="root" password="password" /></source><destination><database host="localhost" name="m2databasename" user="root" password="password" /></destination>7. Remove .dist from config.xml from <option>8. Remove .dist from file name vendor/magento/data-migration-tool/etc/opensource-to-opensource9. php bin/magento migrate:settings -r -a vendor/magento/data-migration-tool/etc/opensource-to-opensource/1.9.2.3(M1 Version)/config.xml10. php bin/magento migrate:data -r -a vendor/magento/data-migration-tool/etc/opensource-to-opensource/1.9.2.3(M1 Version)/config.xml11. php bin/magento migrate:delta -r -a vendor/magento/data-migration-tool/etc/opensource-to-opensource/1.9.2.3(M1 Version)/config.xml

https://www.mageefy.com/blog/post/data-migration-steps-from-magento1-to-magento2