This study aims to use the Problem-based Learning (PBL) method associated with social constructivism to enhance student readiness and achievement for high school English in online learning in China. Considering those in the context of the pandemic, teaching is shifting to online but lacking in more effective interaction. This pedagogy is applied in quasi-experiment research in Guiyang city, Guizhou province. Paired sample t-test is conducted in the experiment on students’ readiness and results show a positive increase ( M = 6.24) after the intervention t (49) = 6.77, p = .001 ( p < .05), and a significantly raising in dimensions of social competencies with classmates are M = 3.56, t (49) = 6.89, p = .001, communication competencies are M = 2.38, t (49) = 5.81, p = .001 respectively. Furthermore, a significant difference is found in students’ achievement post-test when covariate the pre-test, F (1, 97) = 11.46, p = .001, partial eta squared = .11. Students’ readiness can be improved when adopting the PBL techniques and activities through online learning. This approach has proven helpful, adaptable, and beneficial to learn English, especially for high school students who are forced to study online.