Time out issues

I have a program which will retrieve the accounting information, the result as like as T-code F.19, but when i execute the program it will caused time out issue, I have not idea how to solve it. Could you help. Here is the source code which cause time out. Thank!

select * from bsis

into corresponding FIELDS OF table it_bsis

where bukrs in so_bukrs and

budat in so_budat and

augdt = '00000000' and

dmbtr ne 0.

loop at it_bsis.

select single * from bseg

where bukrs = it_bsis-bukrs and

belnr = it_bsis-belnr and

gjahr = it_bsis-gjahr and

buzei = it_bsis-buzei and

ebeln in so_ebeln and

matnr in so_matnr and

hkont in so_hkont.

if sy-subrc = 0.

MOVE-CORRESPONDING BSEG TO BSIS_TAB.

BSIS_TAB-WAERS = it_bsis-WAERS.

BSIS_TAB-BUDAT = it_bsis-BUDAT.

BSIS_TAB-BLART = it_bsis-BLART.

IF it_BSIS-SHKZG = 'H'.

BSIS_TAB-DMBTR = 0 - BSEG-DMBTR.

BSIS_TAB-DMBE2 = 0 - BSEG-DMBE2.

BSIS_TAB-DMBE3 = 0 - BSEG-DMBE3.

BSIS_TAB-WRBTR = 0 - BSEG-WRBTR.

ENDIF.

APPEND BSIS_TAB.

endif.

endloop.