GET "/projects/:id/pipelines/:pipeline_id/jobs" returns nothing

I’m using a private hosted enterprise Gitlab version 11.11
I’m trying to use gitlab APIs to query repository pipeline running result details. According to document, I should be able to get the pipeline job list by GET /projects/:id/pipelines/:pipeline_id/jobs. While, in my practice,I can get correct information with GET /projects/:id/pipelines/:pipeline_id, but only got a “” with GET /projects/:id/pipelines/:pipeline_id/jobs. From the UI, I can see very clear that there is one job under this pipeline. Why I couldn’t get a list of jobs with this API?