Yan Zhenqing's calligraphy is exquisite and good at it. Chu Suiliang, a beginner, studied under Zhang Xu and got his brushwork.
Its regular script is dignified and majestic, and its running script is vigorous and powerful, which has created a "Yan style" regular script and has a great influence on later generations.
Together with Zhao Mengfu, Liu Gongquan and Ou Yangxun, they are also called "four masters of regular script".
His calligraphy style is called "Yan Ti", which is also called "Yan Liu" with Liu Gongquan, and has the reputation of "Yan Liu Jin Gu".
References:
Baidu Encyclopedia-Yan Zhenqing