I'm not quite sure what you're asking:

Do you mean you want to jump <i>from</i> assembler <i>to</i> your 'C' program?
Or do you want to insert an "LJMP 000h" instruction into your 'C' program.

<i>"got error in compiling"</i>

OK, what error did you get?
Please show a code excerpt, and the <b>full</b> error message (including the error number)

When posting the code, remember to enclose it within the HTML < pre > and < /pre > tags - then it'll format properly.
(but don't use the extra spaces like I just did - that was just so you could see the actual tags!)

When debugging error messages, remember that you must always resolve the first message first, before moving on to subsequent messages - as one error will often cause more errors later in the file!

Have you read the section <i>"Interfacing C Programs to Assembler"</i> in the Keil C51 manual, and the section <i>"Interfacing to Assembly"</i> in the Getting Started with µVision2 manual?