With the rapid development of related technology, the virtual reality is attracting increasing attention. As an intuitive object for human-computer interaction, the virtual human plays an important role in the virtual environment. During the process of building plausible virtual human, one crucial step is to create emotional facial expressions. The mainstream methods often rely on hand-crafted efforts by designers, resulting a laborious and time-consuming task. To address this problem, this paper introduces a method that generates emotional expressions based on manipulating blendshapes. Given an arbitrary facial expression image, this method estimates the corresponding blendshape coefficients, which can be used to generate the target emotional expression on the virtual human face. Experiment results show that the proposed method has strong generalization ability and is effective on reducing the burden of human designers in the task of emotional expressions generation.