The 3D animation automatic generation system of mobile phone aims to obtain an animation which matches an input text message and send it to the recipient. Expressions in animation are important for expressing emotional themes and enhancing animation effects. This study focuses on the automatic generation of the character expression in the 3D animation system, mainly including the qualitative planning and the quantitative calculation. The qualitative planning part mainly uses the semantic Web technology to build an expression ontology library based on the facial coding system and the emotional wheel model and establish the appropriate axioms. Then knowledge reasoning is carried out according to the key information of short message to get the qualitative description of expressions. Followed is converting the qualitative description information into specific animation data and processing the expression smooth transition in the quantitative part, and finally a rich and diverse character expression animation is generated. Except for the abnormalities caused by human operation in the 270 data of the experiment, the success rate of expression planning is 71.2%, and the diversity expression generation rate is 83.76%. Experiments show that this proposed method can generate expression animations better.