$re = '/<my:group1>(.*)<\/my:group1>/s';
$str = '<?xml version="1.0" encoding="UTF-8"?>
<?mso-infoPathSolution solutionVersion="1.0.0.182" productVersion="15.0.0" PIVersion="1.0.0.0" href="http://sp01/hp/Therapy/Forms/template.xsn" name="urn:schemas-microsoft-com:office:infopath:Therapy:-myXSD-2013-03-01T10-07-30" ?>
<?mso-application progid="InfoPath.Document" versionProgid="InfoPath.Document.3"?>
<my:myFields
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:pc="http://schemas.microsoft.com/office/infopath/2007/PartnerControls"
xmlns:ma="http://schemas.microsoft.com/office/2009/metadata/properties/metaAttributes"
xmlns:d="http://schemas.microsoft.com/office/infopath/2009/WSSList/dataFields"
xmlns:q="http://schemas.microsoft.com/office/infopath/2009/WSSList/queryFields"
xmlns:dfs="http://schemas.microsoft.com/office/infopath/2003/dataFormSolution"
xmlns:dms="http://schemas.microsoft.com/office/2009/documentManagement/types"
xmlns:xhtml="http://www.w3.org/1999/xhtml"
xmlns:my="http://schemas.microsoft.com/office/infopath/2003/myXSD/2013-03-01T10:07:30"
xmlns:xd="http://schemas.microsoft.com/office/infopath/2003"
xml:lang="en-us">
<my:PatientID>1</my:PatientID>
<my:Name>name</my:Name>
<my:Age>29.0000000000000</my:Age>
<my:Gender>gender</my:Gender>
<my:Date>2015-12-09</my:Date>
<my:group1>
<my:group2>
<my:field1>1</my:field1>
<my:PName>pname</my:PName>
<my:PPrice>10000.0000000000</my:PPrice>
<my:field11 xsi:nil="true"></my:field11>
</my:group2>
<my:group2>
<my:field1>9</my:field1>
<my:PName>pname
</my:PName>
<my:PPrice>10000.0000000000</my:PPrice>
<my:field11 xsi:nil="true"></my:field11>
</my:group2>
</my:group1>
<my:field4></my:field4>
<my:field5></my:field5>
<my:Status>false</my:Status>
<my:Confirm>false</my:Confirm>
<my:field6></my:field6>
<my:field7></my:field7>
<my:field8></my:field8>
<my:TPrice>20000</my:TPrice>
<my:field12></my:field12>
<my:field13></my:field13>
<my:insurance>1</my:insurance>
<my:Partner>partner</my:Partner>
<my:Doctor>doctor</my:Doctor>
</my:myFields>';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php