The laser Doppler technique is a kind of non-contact velocimetry,which has many advantages,such as high precision,wide speed range,high spatial resolution.It does not affect the flow field and can be used in measuring long-range velocity field.Therefore,Doppler velocimetry has been used widely in many fields.This article gives a theoretical analysis of laser Doppler velocimetry,and introduces the working mechanism.We also give an analysis of the feasibility of applying the laser Doppler velocimetry to flow field in internal combustion engine.Finally we introduce the domestic and international developments of Doppler velocimetry of flow field in internal combustion engine.