本文基于评价理论中的态度系统，对美国主流媒体关于中国新型冠状病毒疫苗的新闻报道进行定性和定量分析，旨在揭示媒体通过新闻报道所反映出的态度情况，以及其态度是否发生了历时变化。以来自美国三家主流媒体机构的133篇报道为语料自建语料库，在AntConc语料库工具的帮助下，通过对关键词、搭配词以及索引行的分析，提取出177个态度资源。将态度资源分类归入情感、判断、鉴赏三个子系统，进一步分析不同类别资源的频率和分布情况。

    研究结果表明：（1）在所有态度资源中，判断资源占比52.6%，鉴赏资源占比31.6%，情感资源占比15.8%。超过半数的态度资源属于判断子系统，这体现美国主流媒体对中国新型冠状病毒疫苗在社会道德和社会影响方面的尤其关注。（2）在所有态度资源中，表达负面意义的资源占比59.9%，表达正面意义的资源占比40.1%。美国主流媒体对中国新冠疫苗大体上持负面态度。（3）在从2020年至2022年的两年间，表达正面意义的态度资源占比呈现上升趋势，负面资源占比则随之呈下降趋势。随着时间推移与社会背景的变化，美国主流媒体对中国新冠疫苗的态度有所缓和。

Based on the attitude system in Appraisal Theory, this paper attempts to analyze the news reports from American mainstream media about China’s COVID-19 vaccines both qualitatively and quantitatively. The goal is to reveal the media’s attitudes and to explore whether the attitudes undergo diachronic changes. A corpus containing the data from 133 pieces of reports in three media organizations is built. By means of analyzing the Keyword list, collocates, and concordance lines with the help of the AntConc corpus tool, 177 attitudinal resources are extracted and classified into three subsystems: affect, judgment, and appreciation. The frequencies and distributions of resources under different categories are further analyzed.

The research results show that: (1) Among all the attitudinal resources, the judgment resources account for 52.6%, the appreciation resources account for 31.6%, and the affect resources 15.8%. More than half of the resources belong to the judgment subsystem, suggesting the media’s attention to the aspect of social morality and the significance caused in the society when it comes to China’s COVID-19 vaccines. (2) The negative resources account for 59.9% of all the attitudinal resources, and the positive resources account for 40.1%. Generally, the American mainstream media holds a negative attitude toward China’s vaccines. (3) From 2020 to 2022, the proportion of positive resources in the two years has shown an increasing tendency and that of the negative resources is accordingly decreasing. The American mainstream media’s position has softened as time goes by and the social background changes.