I am trying to create a terraform script which will create a vpc and other resources. I am passing the parameters for scripts from a .tfvars file. I have successfully created the vpc and resources by executing the script. Now I want to create another vpc with same set of resources but with different set of parameter values. I have created a new .tfvars file with new values and tried to execute it with the old main.tf file. When I execute the 'terraform plan' command its showing that it will delete the vpc and resources created during my first run will create a new vpc with the new values. Is there any method to create resources using same terraform main.tf file and by changing the .tfvars file.
You are running into a state-based issue. When you define a resource you give it a name. Those names are used in the state file and that is what is making Terraform to think you are trying to alter an existing resource. You have a couple of ways to address this and it depends on what you are really doing.
Terraform Workspaces
You could use workspaces in terraform for each VPC you are creating, this would keep the state separated, however, workspaces are really intended to separate environments, not multiple resources in the same environment. You can read more here.
Terraform Modules
What it sounds like to me is that you really want to create a terraform module for your VPC configuration. Then create each VPC using your module in the same main.tf. That way you will have unique names resources which will not confuse the state management. You can read more about modules here. A good resource for information about it can be found in this blog post.