following tye's comments it's works ok, but bulk88's can't work. I don't know why. follow is my corrected code:

#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"
#include "ppport.h"
#include "const-c.inc"
#include "top_insert.h"

MODULE = top_insert            PACKAGE = top_insert 

INCLUDE: const-xs.inc


void
top_insert(up_v, up_num, down_v, down_num, init_step_ratio, ratio)
        char * up_v
        int up_num
        char * down_v
        int down_num
        double init_step_ratio
        double ratio
    INIT:
        int sample_num;
        int n;
        double *return_val = NULL;
    PPCODE:
        return_val = get_inter_line(up_num, (double *)up_v, down_num, 
+(double *)down_v,
            init_step_ratio, ratio, &sample_num);
        sample_num = sample_num*3;
        for (n=0; n<sample_num; n++){
            XPUSHs(sv_2mortal(newSVnv(*(return_val + n))));
        }
        del_inter_line(return_val);
[download]

Thanks both of you very much.

BTY, I use those pretty complex. c++ code buld to static lib for quickly algorithm. xs code link to perl mod. use perlctrl pack pm to Win32::OLE dll. use autoCad autoLisp to call OLE. so difficult to debug.