The invention belongs to the technical field of animal husbandry machinery, and relates to a rumen pH meter. The rumen pH meter comprises a pH meter probe, a guide tube, a pH display, a controller and a clamp. In the pH meter probe, a pH meter electrode is arranged on an electrode support, the electrode support is fixedly connected outside an electrode casing at the window of the electrode casing, and during the process that the pH meter probe is inserted into the rumen through an oral cavity and an esophagus of a ruminant, in order to avoid contamination of saliva and esophagus mucus during insertion process, the pH meter probe is closed, and the pH meter electrode is sealed. When the rumen pH meter probe works, the pH meter probe is open to expose the window of the electrode casing, and the pH meter electrode is exposed in a gastric fluid environment to measure the pH of rumen fluid in the rumen. The rumen pH meter provided by the invention can conveniently and rapidly measure the pH value of the rumen, has low cost and high practicability, has good effects in early diagnosis and prevention in advance of ruminal acidosis, and is suitable for monitoring the gastric pH value in the rumen of the ruminant during scientific research and production.