using System;
using System.Diagnostics;
using System.Net;
using System.Runtime.InteropServices;


namespace clicksun
{
    class PortCloser
    {
        [StructLayout(LayoutKind.Sequential)]
        public struct MIB_TCPROW_OWNER_PID
        {
            public uint state;
            public uint localAddr;
            public uint localPort;
            public uint remoteAddr;
            public uint remotePort;
            public uint owningPid;
        }


        [DllImport("iphlpapi.dll", SetLastError = true)]
        static extern uint GetExtendedTcpTable(
            IntPtr pTcpTable,
            ref int pdwSize,
            bool bOrder,
            int ulAf,
            TCP_TABLE_CLASS tableClass,
            uint reserved = 0);


        public enum TCP_TABLE_CLASS
        {
            TCP_TABLE_OWNER_PID_ALL = 5
        }


        public static void ClosePort(int targetPort)
        {
            int bufferSize = 0;
            GetExtendedTcpTable(IntPtr.Zero, ref bufferSize, true, 2, TCP_TABLE_CLASS.TCP_TABLE_OWNER_PID_ALL);
            IntPtr tcpTablePtr = Marshal.AllocHGlobal(bufferSize);
            try
            {
                uint ret = GetExtendedTcpTable(tcpTablePtr, ref bufferSize, true, 2, TCP_TABLE_CLASS.TCP_TABLE_OWNER_PID_ALL);
                if (ret != 0) throw new Exception("获取TCP表失败，错误代码: " + ret);


                int entryCount = Marshal.ReadInt32(tcpTablePtr);
                IntPtr rowPtr = (IntPtr)((long)tcpTablePtr + 4);
                for (int i = 0; i < entryCount; i++)
                {
                    MIB_TCPROW_OWNER_PID row = (MIB_TCPROW_OWNER_PID)Marshal.PtrToStructure(rowPtr, typeof(MIB_TCPROW_OWNER_PID));
                    rowPtr = (IntPtr)((long)rowPtr + Marshal.SizeOf(typeof(MIB_TCPROW_OWNER_PID)));


                    ushort port = (ushort)IPAddress.NetworkToHostOrder((short)row.localPort);
                    if (port == targetPort)
                    {
                        try
                        {
                            Process process = Process.GetProcessById((int)row.owningPid);
                            process.Kill();
                            Console.WriteLine($"已终止进程: {process.ProcessName} (PID: {process.Id})");
                        }
                        catch (ArgumentException)
                        {
                            Console.WriteLine($"未找到PID为 {row.owningPid} 的进程。");
                        }
                        catch (Exception ex)
                        {
                            Console.WriteLine($"终止进程时出错: {ex.Message}");
                        }
                    }
                }
            }
            finally
            {
                Marshal.FreeHGlobal(tcpTablePtr);
            }
        }
    }
}

使用方法：

PortCloser.ClosePort(3389);   //强制关闭3389端口的所有连接