i have one abs file , and i want to convent it to bin or hex file . how can i do it?
I'm not sure off the top of my head what a .abs file is ("absolute" would seem to mean the same as "binary" to me). But take a look at http://srecord.sourceforge.net It's a flash programmer file conversion utility that can convert between about 28 file formats (and do other sorts of tricks for chopping them up and rearranging them).
Converting .abs to .hex is what Keil's OHx51 utility (part of your C51 toolchain) does. Check your Assembler/Utilities manual.