During the 1990s CALT developed an improved version of the DF-4 to test the reentry vehicle warheads of the DF-31. They took advantage of this development and offered it as the Long March 1D for commercial application. The modification included:

• An DF-4 improved first stage, which used the new version of the YF-2B, and switched propellants to UDMH/N₂O₄ for improved performance.
• The use switch of the second stage YF-3A, for the Long March 4 third stage engine, the YF-40.
• A new, cylinder interstage between the second and third stage, which enabled to add RCS to the third stage. The olde one was tapered.
• A new third stage with a new motor, the FG-36 and an optional RCS.
• A new computer inertial guidance system which enabled the third stage to be 3-axis stabilized for added precision.