is_tag()

function is_tag( $tag = '' ) {
	global $gc_query;

	if ( ! isset( $gc_query ) ) {
		_doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '3.1.0' );
		return false;
	}

	return $gc_query->is_tag( $tag );
}

// When any Tag archive page is being displayed.
is_tag();

// When the archive page for Tag 30 is being displayed.
is_tag( '30' );

// When the archive page for tag with the Slug of 'extreme' is being displayed.
is_tag( 'extreme' );

// When the archive page for tag with the Name of 'mild' is being displayed.
is_tag( 'mild' );

/*
 * 响应s true when the tag of posts being displayed is either term_ID 30,
 * or slug "extreme", or name "mild". Note: the array ability was added
 * at Version 3.7.
 */
is_tag( array( 30, 'mild', 'extreme' ) );