The invention discloses a method and a device for detecting a water oxygen infiltration index in device packaging. The method comprises the following steps of: firstly, preparing a quartz crystal plated with an active metal layer; secondly, transferring the quartz crystal to a test box under the condition that air is isolated and sealing by using a packaging structure and a packaging method the same as the device packaging; and finally, connecting the test box with a crystal oscillator, a crystal controller and a power supply to form a quartz microbalance, switching on the power supply, sensing the piezoelectric effect and mass loading effect of the quartz crystal through the crystal controller, outputting the piezoelectric effect and mass loading effect to the microbalance in real time, calculating the increased mass of a metal film after infiltrated water is absorbed and then calculating the water oxygen infiltration rate and total infiltrated water oxygen content in unit time. The method and the device can be used for detecting the water oxygen infiltration rate in real time on line in the packaging of a water oxygen sensitive device, have the detection limit of lower than 5*10<-6>g.m<-2> / d, and can meet the limit detection requirement of packaging of organic photoelectric device products on water gas infiltration rate.