Magento 1 : Add Order Status in system configuration

Add source model “adminhtml/system_config_source_order_status” to get the list of order statuses.

The below code will show you the multi select box where you can select more than one order statuses

<order_status translate="label">
  <label>Order Statuses</label>
  <frontend_type>multiselect</frontend_type>
  <source_model>adminhtml/system_config_source_order_status</source_model>
  <sort_order>3</sort_order>
  <show_in_default>1</show_in_default>
  <show_in_website>1</show_in_website>
  <show_in_store>0</show_in_store>
</order_status>

The below code will show you the select box where you can select one order status

<order_status translate="label">
  <label>Order Status</label>
  <frontend_type>select</frontend_type>
  <source_model>adminhtml/system_config_source_order_status</source_model>
  <sort_order>3</sort_order>
  <show_in_default>1</show_in_default>
  <show_in_website>1</show_in_website>
  <show_in_store>0</show_in_store>
</order_status>