A novel detector with confocal optical configuration was fabricated for detecting the weak emission light of infrared up-conversion material.The following approaches were imploemented for increasing the sensitivity of the detector.Based on the characteristics of emission spectrum of the up-conversion material,the special designed optical splitter was used to reflect the infrared beam into a confocal optical device,then the excited visible light with higher intensity returns to pass through this optical splitter with high transmission into GaAsP device,which has the high sensitivity to visible light and total cut-off to the infrared light.This detector with amplification circuits can be sensitive to the emission light from the up-conversion material with over 0.3% mixing ratio to ink.The results of detecting the IR ink marks of different mixing ratios wre given.