A food safety testing instrument is designed and developed based microcontroller. The instrument includes optical unit, conditioning unit and control and acquisition unit. The optical unit converts the chemiluminescence signals into electrical signals through photoelectric sensor. Conditioning circuit mainly amplifies the weak signal to an appropriate range. Control and data acquisition circuit consists of the MCU, LCD and memory circuit. The experiment shows that the correlation coefficient (R2) between the phosphate ion concentration and emitting area was 0.98. The instrument is small，cheap and reliable. It shows that the instrument can successfully used to quick measurement for food safety in field.