Sy-tabix is used to find the current line in the internal table; it’s a current line index. Whereas sy-index in used to find the number of current pass in the loop statement.
sy-tabix = Index of Internal Tables
set by commands processing internal tables (e.g. READ, LOOP)
It contains the nr/index of the last line accessed for standard or sorted tables. In case of hashed tables it is set to 0
since hashed tables are no index tables, they use a hash administration.
sy-index = Loop Index.
set by DO and WHILE loops. contains the number of the loop passes including the current pass.
sy-tabix is nothing but the index or row number of an internal table.
Suppose, you loop through an internal table , so the sy-tabix will be set as the row number of the table.
when control goes to the twentieth record of the table, then sy-tabix will hold value 20.
On otherhand, sy-index denotes the number of processing for any loop statements like do, while etc.