The result difference of osmotic pressure test of formula food for special medical purpose by different instruments and different methods, and osmotic pressure status of all kinds of formula food for special medical purpose at domestic and abroad at present were studied. 38 samples of formula food for special medical purpose at domestic and abroad were collected and tested with German GONOTEC 3000-D osmometer. Some representative samples were selected to use other freezing point instruments and dew point instruments for instrument comparison and method comparison at the same time. The range for osmotic pressure test results of 38 samples determined by freezing point method was 89 mOsmol/kg~869 mOsmol/kg, and the relative standard deviation was 0.25%~0.97%; among the samples for comparison, the average range for the test results of freezing point method was 168 mOsmol/kg~640 mOsmol/kg, and the relative standard deviation was 0.18%~1.70%; the average range for the test results of dew point method was 162 mOsmol/kg~594 mOsmol/kg, and the relative standard deviation was 0.61%~4.81%. The samples with high osmotic pressure were mainly amino acid formula and total nutrition formula, and the infants formula samples results of osmotic pressure test were low; the result of dew point method was lower than that of freezing point method, and the stability and repeatability of the test results were not as good as the freezing point method. The detection error can be reduced by keeping the temperature and humidity of the environment and the stability of the instrument, and using reasonable injection quantity.