#include <stdio.h>
#include <stdlib.h>

#define TURE 1
#define FALSE 0
#define Max 20
typedef struct                    
{
     float coef;                    /*系数*/
    int expn;                     /*指数*/
}ElemType;

typedef struct LNode                 
{
    ElemType data;                    
    struct LNode *pNext;         
}LNode, *Ploynomial;

int InitList(Ploynomial pList)
{
     pList = (Ploynomial ) malloc (sizeof (LNode));                /*创造头节点*/
    pList -> pNext = NULL;
    pList -> data.coef = 0.0;
    pList -> data.expn = 0;
    return TURE;
}

int DestroyList(Ploynomial pList)
{
     Ploynomial p = pList, q = p -> pNext;
    while (q != NULL)
    {
           free(p);
          p = q;
          q = p -> pNext;      
    }
    free(p);     
    return TURE;
}

main()
{
       Ploynomial List;
       printf ("...\n");
      InitList(List);
      DestroyList(List);
      
      system ("pause");      
}
运行结构。。
多项式运行环境.exe已停止工作

#include <stdio.h>
#include <stdlib.h>

#define TURE 1
#define FALSE 0
#define Max 20
typedef struct                    
{
     float coef;                    /*系数*/
    int expn;                     /*指数*/
}ElemType;

typedef struct LNode                 
{
    ElemType data;                    
    struct LNode *pNext;         
}LNode, *Ploynomial;

int InitList(Ploynomial &pList)//加& pList在调用时才会在函数中变化，发生改变
{
     pList = (Ploynomial ) malloc (sizeof (LNode));                /*创造头节点*/
    pList -> pNext = NULL;
    pList -> data.coef = 0.0;
    pList -> data.expn = 0;
    return TURE;
}

int DestroyList(Ploynomial &pList)//这里也一样
{
     Ploynomial p = pList, q = p -> pNext;
    while (q != NULL)
    {
          free(p);
          p = q;
          q = p -> pNext;       
    }
    free(p);     
    return TURE;
} 

int main()//改
{
       Ploynomial List;
       printf ("...\n");
      InitList(List);
      DestroyList(List);
      
      system ("pause");      
      return 0;//加
}
//你的里面也没存数，只有一个表头。我是这样想的，你看看吧。欢迎批评

Ploynomial pList   就相当于 LNode * pList吧！！
  那你在给pList 前面加个&  是不是双重指针了  ？

指针的引用，主要是为了传递的是指针的地址而不是指针值

#include <stdio.h>
#include <stdlib.h>
#define TURE 1
#define FALSE 0
#define Max 20
typedef struct                  

 {
      float coef;                    /*系数*/
     int expn;                     /*指数*/

 }ElemType;
typedef struct LNode               

 {
     ElemType data;                  
     struct LNode *pNext;       

 }LNode, *Ploynomial;
int InitList(Ploynomial pList)//要么外面分配好的内存传进来，要么里面分配好的内存用返回值把指针返回去，外面穿指针，里面再给它分配内存，毫无意义
{
     
     pList -> pNext = NULL;
     pList -> data.coef = 0.0;
     pList -> data.expn = 0;
     return TURE;

 }
int DestroyList(Ploynomial pList)//从最后一个结点开始往前释放
{
     Ploynomial p = pList, q = p -> pNext;
     while ( p != NULL)
     {
            if (p->pNext != NULL){
                     p = p->pNext;
                    continue;
            }
           free(p);
           p = pList;     
     }
    
     return TURE;

 }

int main()
{
        Ploynomial List;
        List = (Ploynomial ) malloc (sizeof (LNode));                /*创造头节点*/
        printf ("...\n");
       InitList(List);
       DestroyList(List);
     
       system ("pause");    
       return 0;
}
没有在机子上跑，小改下，不知道有木有错误，谅解！