In　this　paper,　the　temperature　dependence　of　birefringence　in　polarization　maintaining　photonic　crystal　fibres　(PM-PCFs)　is　investigated　theoretically　and　experimentally.　Utilizing　the　structural　parameters　of　the　PM-PCF　samples　in　the　experiment,　two　effects　leading　to　the　birefringence　variation　under　different　temperatures　are　analysed,　which　are　the　thermal　expansion　of　silica　material　and　the　refractive　index　variation　due　to　the　temperature　variation.　The　actual　birefringence　variation　of　the　PM-PCF　is　the　combination　of　the　two　effects,　which　is　in　the　order　of　10(-9)　K-1　for　both　fibre　samples.　Calculation　results　also　show　that　the　influence　of　refractive　index　variation　is　the　dominant　contribution,　which　determines　the　tendency　of　the　fibre　birefringence　variation　with　varying　temperature.　Then,　the　birefringence　beat　lengths　of　the　two　fibre　samples　are　measured　under　the　temperature,　which　varies　from　-40　degrees　C　to　80　degrees　C.　A　traditional　PANDA-type　polarization　maintaining　fibre　(PMF)　is　also　measured　in　the　same　way　for　comparison.　The　experimental　results　indicate　that　the　birefringence　variation　of　the　PM-PCF　due　to　temperature　variation　is　far　smaller　than　that　of　the　traditional　PMF,　which　agrees　with　the　theoretical　analysis.　The　ultra-low　temperature　dependence　of　the　birefringence　in　the　PM-PCF　has　great　potential　applications　in　temperature-insensitive　fibre　interferometers,　fibre　sensors,　and　fibre　gyroscopes.