在.NET Core 3.0及更高版本中，可以使用Roslyn API来读取和分析C#代码，然后操作代码并删除未使用的using语句。以下是一个示例：

1.创建一个.NET Core Console应用程序。

2.添加以下NuGet包：

Microsoft.CodeAnalysis.CSharp

Microsoft.CodeAnalysis.VisualBasic

Microsoft.CodeAnalysis.Workspaces.Common

3.使用以下代码删除未使用的using：

using System; using System.IO; using System.Linq; using Microsoft.CodeAnalysis; using Microsoft.CodeAnalysis.CSharp; using Microsoft.CodeAnalysis.CSharp.Syntax; using Microsoft.CodeAnalysis.MSBuild;

namespace RemoveUnusedUsings { class Program { static void Main(string[] args) { string solutionFilePath = args[0];

        // Load the solution and wait for it to fully load
        using (var workspace = MSBuildWorkspace.Create())
        {
            var solution = workspace.OpenSolutionAsync(solutionFilePath).Result;

            // Go through each project in the solution
            foreach (var project in solution.Projects)
            {
                // Create a compilation for the project
                var compilation = project.GetCompilationAsync().Result;

                // Go through each syntax tree in the compilation
                foreach (var syntaxTree in compilation.SyntaxTrees)
                {
                    // Parse the syntax tree and get the root node
                    var syntaxRoot = syntaxTree.GetRoot();

                    // Find all using directives
                    var usingDirectives = syntaxRoot.DescendantNodes().OfType();

                    // Get the semantic model for the syntax tree
                    var semanticModel = compilation.GetSemanticModel(syntaxTree);

                    // Go through each using directive
                    foreach (var usingDirective in usingDirectives)
                    {
                        // Get the symbol for the using directive
                        var symbol = semanticModel.GetSymbolInfo(usingDirective.Name).Symbol;

                        // If the symbol is null or not a namespace, remove the using directive
                        if (symbol == null || symbol.Kind != SymbolKind.Namespace)
                        {
                            syntaxRoot = syntaxRoot.RemoveNode(usingDirective, SyntaxRemoveOptions.KeepUnbalancedDirectives);
                        }
                    }

                    // Write the syntax tree back to the source file
                    File.WriteAllText(syntaxTree.FilePath, syntaxRoot