Pl go thru the following may be useful
The lowest level that a material appears in any product structure of the
company. The low-level code controls the sequence in which the material
is planned in an MRP run: First the materials with low-level code 0 are
planned, then the materials with low-level code 1, and so on. The lower
the low-level code, the higher the number that is assigned to the
The level that is set in the material master record represents the level
at which the material will be planned. This means that the material will
only be planned once all assemblies in which it occurs have been planned
The low-level code is set internally in the material master record when
the BOM is maintained.
When you create a bom item for a assemblyparts ,the item's low-level code will equal (assemblyparts's low-level code + 1),but if (assemblyparts's low-level code + 1) < bom item then the bom item's low-level code not changed
Depending upon the BOM structure, System will automatically assign the low level code.
You can see it in Material Master, Information (Blue Button).
Please refer this link,