A projectile-velocity measurement system using novel laser diode screen is introduced.After collimated and spread

the light of LD is projected to the Scotchlite retroreflector

and then reflected to form a spot with certain diameter.An fiber optic taper is used to transform the spot with larger diameter into smaller one

which is then received by a photodiode.In addition

the reflectivity measurement method and result of Scotchlite retroreflector is presented in the paper.Finally

the waveform of 3 mm flying object has been presented.The experiment result indicates that the photoelectric detecting system with Scotchlite retro-reflector and fiber optic taper has high S/N ration and sensitivity.