The invention provides a quick test method used for testing formaldehyde in the yoghourt. First, absorbing 2.0-2.8ml sample of the yoghourt into a capped colorimetric cylinder, then adding 0.005-0.02mol/L AGAO3 solution 0.5-5ml and 0.01-0.5mol/L NaOH solution 1.0-10.0ml into the the sample, drawing the plug after shaking the solution uniformly, successively, placing the tube into the beaker which contains boiling water for 0.5-5 minute., then, removing the beaker and observing the change of color in the cylinder.,the occurenceog different depth of coffee color indicating that the sample contains formaldehyde, while the occurence of a pale yellow color indicating formaldehyde negative. The invention is based on the principle that in alkaline environment AgNO3 can be deoxidized into Ag. Adding AgNO3 and NaOH solution into fresh milk, whether the sample contains formaldehyde can be determined by different color-developing effect. The test is quick and highly sensitive, the color-developing is distinct, and the positive result is easy to grasp.It is also adapts to outdoors, farms, purchase or sale sits and easy to popularization and application. The lowest test limit is 7.6mug/ml yoghurt.