Abstract: The dynamic linearity is an important technical parameter for instantaneous radiation pyrometer, which has great impact on measurement accuracy. In order to study the factors which influence the dynamic linearity of radiation pyrometer, a test technique is proposed for measuring pulse dynamic linearity, which is based on pulse LED and high linearity photodetector. An instantaneous radiation pyrometer，based on photomultiplier tubes (PMT)，is tested and measured under various conditions. The measurement results show that the factors such as PMT type, voltage divider and operation voltage have impact on the dynamic current linearity of pyrometer.