@Surbhi Srivasta 

update as this and it will work fine.

UI Action

function openPage() {

	var dd = new GlideDialogWindow('UI Page Name');
	//dd.setTitle(getMessage(""));
	dd.setWidth(800);
	dd.setPreference('sysparm_record', g_form.getUniqueValue());
	dd.setPreference('sysparm_recordDisplayValue', g_form.getValue('number'));
	dd.setPreference('sysparm_record_table', g_form.getTableName());
	dd.render();
}

UI Page HTML:

<g:evaluate var="jvar_current" expression="RP.getParameterValue('sysparm_record')"/>
<g:evaluate var="jvar_current_table" expression="RP.getParameterValue('sysparm_record_table')"/>
<g:evaluate var="jvar_currentRecordDisplayValue" expression="RP.getParameterValue('sysparm_recordDisplayValue')"/>

<table>
<tr>
<td style="width:25%;padding:5px;">
<g:form_label>Preview Record</g:form_label>
</td>
</tr>
<tr>
<td class ="paddingBetweenCols" style="width:60%">
<g:ui_reference name="rec_details" id="rec_details" value="${jvar_current}" table="${jvar_current_table}" displayValue="${jvar_currentRecordDisplayValue}"/>
</tr>
</table>