解决了！原因是破坏了原来的链表结构。

class Solution {
public:
    RandomListNode* Clone(RandomListNode* pHead)
    {
        if(pHead==nullptr)
            return pHead;
       RandomListNode* head=new RandomListNode(0);
        RandomListNode* p=head;
        RandomListNode* cur=pHead;
        //复制
       while(cur)
       {
           p->next=cur;
           p=p->next;
           cur=cur->next;
           RandomListNode* newhead=new RandomListNode(p->label);
           p->next=newhead;
           p=p->next;
       }
        cur=head->next;
        p=cur->next;
        //链接指针
       while(cur)
       {
           if(cur->random)
               p->random=cur->random->next;
           else
                p->random=cur->random;
           cur=p->next;
           if(cur)
               p=cur->next;
       }
        cur=head;
        p=cur->next;
        //拆分
        RandomListNode* keep=new RandomListNode(0);
        RandomListNode* tail=keep;
       while(p)
       {
           cur->next=p->next;
           cur=cur->next;
           tail->next=p;
           tail=p;
           p=cur->next;
       }
        tail->next=nullptr;
        pHead=keep->next;
        return head->next;
    }
};