diff --git a/src/dde-session/main.cpp b/src/dde-session/main.cpp
index db37a7c..1ad0971 100644
--- a/src/dde-session/main.cpp
+++ b/src/dde-session/main.cpp
@@ -90,6 +90,12 @@ int main(int argc, char *argv[])
         DLogManager::registerConsoleAppender();
         DLogManager::registerFileAppender();
 
+        // XDG_CURRENT_DESKTOP=DDE is also injected early by
+        // dde-session-environment.service (Before=graphical-session-pre.target)
+        // to prevent a race where xdg-desktop-portal starts before this call.
+        // EnvironmentsManager::init() still runs here to set the full set of
+        // environment variables (QT_QPA_PLATFORM, scale factors, etc.) and to
+        // call qputenv() for the current process.
         EnvironmentsManager().init();
 
         QString dmService = "dde-session.target";
diff --git a/systemd/CMakeLists.txt b/systemd/CMakeLists.txt
index f92e2e3..0648555 100644
--- a/systemd/CMakeLists.txt
+++ b/systemd/CMakeLists.txt
@@ -10,6 +10,12 @@ configure_file(dde-session-shutdown.service.in
 configure_file(dde-keyring.service.in
                dde-keyring.service
                @ONLY)
+configure_file(dde-session-environment.service.in
+               dde-session-environment.service
+               @ONLY)
+configure_file(dde-session-environment.sh.in
+               dde-session-environment.sh
+               @ONLY)
 
 
 set(SERVICES
@@ -20,11 +26,20 @@ set(SERVICES
     ${CMAKE_CURRENT_BINARY_DIR}/dde-session-exit-task.service
     ${CMAKE_CURRENT_BINARY_DIR}/dde-session-shutdown.service
     ${CMAKE_CURRENT_BINARY_DIR}/dde-keyring.service
+    ${CMAKE_CURRENT_BINARY_DIR}/dde-session-environment.service
     dde-session-shutdown.target
     dde-session.target
 )
 install(FILES ${SERVICES} DESTINATION lib/systemd/user/)
 
+# Install the early environment setup script
+install(PROGRAMS ${CMAKE_CURRENT_BINARY_DIR}/dde-session-environment.sh
+        DESTINATION ${CMAKE_INSTALL_LIBEXECDIR}/deepin)
+
+# graphical-session-pre.target.wants - early environment injection
+install(DIRECTORY DESTINATION lib/systemd/user/graphical-session-pre.target.wants/)
+install_symlink(dde-session-environment.service graphical-session-pre.target.wants)
+
 install(DIRECTORY DESTINATION lib/systemd/user/dde-session-pre.target.wants/)
 set(DDE_SESSION_PRE_WANTS
     dde-session-pre.target.wants/dde-session@x11.service
diff --git a/systemd/dde-session-environment.service.in b/systemd/dde-session-environment.service.in
new file mode 100644
index 0000000..4397ecd
--- /dev/null
+++ b/systemd/dde-session-environment.service.in
@@ -0,0 +1,12 @@
+[Unit]
+Description=Set DDE session environment variables early
+RefuseManualStart=yes
+RefuseManualStop=yes
+CollectMode=inactive-or-failed
+
+Before=graphical-session-pre.target
+
+[Service]
+Type=oneshot
+ExecStart=@CMAKE_INSTALL_FULL_LIBEXECDIR@/deepin/dde-session-environment.sh
+Slice=session.slice
diff --git a/systemd/dde-session-environment.sh.in b/systemd/dde-session-environment.sh.in
new file mode 100755
index 0000000..5e7c476
--- /dev/null
+++ b/systemd/dde-session-environment.sh.in
@@ -0,0 +1,17 @@
+#!/bin/sh
+# SPDX-FileCopyrightText: 2026 UnionTech Software Technology Co., Ltd.
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+# Set XDG_CURRENT_DESKTOP=DDE early in the systemd user manager and D-Bus
+# activation environments, before graphical-session-pre.target is reached.
+#
+# This ensures that xdg-desktop-portal (the front-end) can discover the DDE
+# portal backend even if it starts before dde-session's full
+# EnvironmentsManager::init() has run, preventing a race where FileChooser
+# and other portal interfaces are missing on cold boot.
+
+rc=0
+systemctl --user set-environment XDG_CURRENT_DESKTOP=DDE || rc=1
+dbus-update-activation-environment XDG_CURRENT_DESKTOP=DDE || rc=1
+exit $rc