Hi Prem,

 You can achieve this by following below steps.

 Step1: Create SmartBox to store Temp details

First Create a SmartBox to store document details "use this to store temporary details” of docs during document upload. Let’s name this as TempDocsDetails.

• Keep The ID field with Type Auto Number
• And Add another Field “Attach Document” of Type File.

You can add more fields as per your requirement

Step 2: Create ListView with TempDocsDetails SMO as data Source

Create a List View with Name “MultiDocUpload” to add Details in TempDocsDetails , By using TempDocsDetails  SMO as data Source for this.

Step3: Add MultiDocUpload view in SmartForm

Add view MultiDocUpload to smartform and write and unbound rule in smartform for Submit button click

• When Button is Clicked
• For All rows on MultiDocUpload View (Add Condition “for each item in a List View”)
• Add Action to insert document in SharePoint List 
• Then add action “Execute a SmartObject method “to delete records from TempDocsDetails SmartBox.

To Insert document in sharepoint List follow the below steps:

• Create a smartobject around your sharepoint list or library with "create" method on the smartobject to upload the attachment to the list.
• You can Create SMO from both SharePoint and SMO tester Utility.

let me know if it helps.