The invention provides a preparation method of urea detection test paper in dairy and a detection method of urea; urease source powder is taken and mixed with pH indicator with the pKHIn more than 6.8; the mixture is diluted by deioned water and the filter solution or the upper suspension liquid after natural deposition is taken, uniformly fixed on a carrier with good water absorption by the forms of coating, printing or soaking, and dried subsequently, thus forming the urea detection test paper; the detection method of the dairy comprises the steps as follows: firstly, common pH test paper is used for detecting the dairy to be detected; whether the dairy to be detected is in normal pH range 6.3-6.8 or not is checked; if so, the urea detection is directly carried out; if not, the pH valueis adjusted to the normal pH range and the urea detection is carried out subsequently; one piece of urea detection test paper dips the dairy to be detected and the color change of the test paper is observed; if the color of the test paper is not changed, the dairy is qualified; if the color of the test paper changes, the dairy is mixed with the urea, thus carrying out qualitative judgment on the dairy; and the displayed color is compared with a standard colorimetric card, so as to carry out semi-quantitative detection of the urea in the dairy.