try this 

Vf Page:

<apex:page controller="AttachmentUploadController">
<apex:sectionHeader title="Visualforce Example" subtitle="Attachment Upload Example"/>

<apex:form enctype="multipart/form-data">
<apex:pageMessages />
<apex:pageBlock title="Upload a Attachment">

<apex:pageBlockButtons >
<apex:commandButton action="{!upload}" value="Save"/>
</apex:pageBlockButtons>

<apex:pageBlockSection showHeader="false" columns="1" id="block1">
<apex:repeat value="{!attachements}" var="a">
<apex:pageBlockSectionItem >
<apex:outputLabel value="File" for="file"/>
<apex:inputFile value="{!a.body}" filename="{!a.name}" id="file" required="true"/>
</apex:pageBlockSectionItem>
</apex:repeat>
</apex:pageBlockSection>

</apex:pageBlock>
</apex:form>
</apex:page>

Apex Class:

public with sharing class AttachmentUploadController {

public list<Attachment> attachements {get;set;}

public AttachmentUploadController() {
attachements = new list<Attachment>();
Attachment obj1 = new Attachment(Name = 'Attachement 1', ParentId = 'a0190000004J47Y');
attachements.add(obj1);

Attachment obj2 = new Attachment(Name = 'Attachement 2', ParentId = 'a0190000004J47Y');
attachements.add(obj2);

Attachment obj3 = new Attachment(Name = 'Attachement 3', ParentId = 'a0190000004J47Y');
attachements.add(obj3);
}

public PageReference upload() {
try {
insert attachements;
} catch (DMLException e) {
ApexPages.addMessage(new ApexPages.message(ApexPages.severity.ERROR,'Error uploading attachment'));
return null;
}

ApexPages.addMessage(new ApexPages.message(ApexPages.severity.INFO,'Attachment uploaded successfully'));
return null;
}
}

Replace the ParentId with your record id