Speaking is a very important part of English learning, which reflects the students’ ability to express themselves and their comprehensive use of language. The research object of this paper is the students of two parallel classes in the first year of a high school. Test method, questionnaire survey method and classroom observation method were mainly utilized in the experiment for the study. Before and after the experiment, two speaking tests were conducted to verify whether the task-based teaching method could improve students’ oral English. The classroom observation method was used throughout the experiment, based on the lexical and syntactic complexity analyzer in terms of both learning motivation and oral proficiency improvement. To verify whether the task-based teaching method can stimulate students’ interest in oral learning from an objective point of view. After the experiment, a questionnaire survey was conducted for students to find out their attitudes towards speaking learning and task-based teaching method. Finally, and SPSS software was used to analyze the data to draw conclusions. The study shows that the mean value of students’ oral English scores in the experimental class after the teaching experiment (M=50.384) is significantly higher than that of the control class (M=37.612), and there is a significant difference (p=0.001<0.05). It can be seen that the task-based teaching method is more effective in improving students’ oral English achievement.