A method for predicting the eye diagram for a controller area network with a flexible data rate (CAN FD) is proposed in this article. A CAN FD changes a data rate according to the status to overcome the limitation of latency. In other words, when data to be transmitted are accumulated, the CAN FD increases the data rate up to 5 Mb/s. The CAN FD has a bus topology consisting of multiple electronic control units, which results in a significant amount of signal reflection. Thus, the above causes the signal integrity analysis uncertain. To avoid this, this article proposes a simplified model for the CAN FD and the eye diagram prediction method based on it. The proposed method has the deterministic and statistical: the deterministic part uses an iterative single bit response method for bit probabilities of a CAN FD packet, and the statistical part uses a modified double edge response method for the flexible data rate. For verification, this article compares the predicted eye diagram to the measured eye diagram, and they are nearly the same when the CAN FD operates at the nominal data rate of 1 and optional data rate of 2 Mb/s.