Juqu Mengxun, having taken the ducal title, promoted a number of officials who were considered capable, and it was said that the people of his state were pleased.
In 402, with Guzang under a severe famine, Juqu Mengxun attacked Later Liang, causing Lü Long to seek aid from Southern Liang, but before Southern Liang forces could arrive, Lü Long defeated Juqu Mengxun, and Juqu Mengxun made peace with Lü Long, offering him food for famine relief.