I want to execute sql script in c# how can i do this.

Load the script from the file into a string, and set it as the cmdText to an SqlCommand object.
Then call the appropriate command method: ExecuteScalar, ExecuteReader, or ExecuteNonQuery

you can use SMO (Sql server Management Object) by C#.
using the following library to execute this :

using Microsoft.SqlServer.Management.Common;
using Microsoft.SqlServer.Management.Smo;

Sample Code like this :

FileInfo file = new FileInfo("ScriptFile.sql");
string script = file.OpenText().ReadToEnd();
SqlConnection conn = GetSqlConnection(); // create connection
Server server = new Server(new ServerConnection(conn));
server.ConnectionContext.ExecuteNonQuery(script);