An Qingxu withdrew to Yecheng and took up defensive position there. Tang forces converged on Yecheng and put it under siege, but with the Tang forces under 10 different jiedushi, the attack was disorganized. Li Siye was often a leader in the assaults on Yecheng. In spring 759, during one of the attacks on Yecheng's defenses, he was hit by a stray arrow. He rested in the camp, and for some time it appeared that his wound would heal. However, when Tang forces launched a subsequent attack, when Li Siye heard the war drums being played, he yelled out in a loud voice, and suddenly, he bled profusely from his wound and died. When the news reached Emperor Suzong, he was shocked, and issued an edict praising Li Siye. He posthumously created Li Siye the Prince of Wuwei and allowed Li Siye's son Li Zuoguo () to inherit the title.