The Monte Carlo method is a kind of unique calculation method. It can resolve not only the question of define evaluation, but also that of random evaluation. The Monte Carlo area fitting method was applied to UV-spectrophotometry of the multicomponent complex preparations without previous separation. The area of each component of complex preparation within a suitable wavelength range of standard spectrogram was multiplied by certain coefficients, and then the products were obtained to fit the area of the measured multicomponent complex preparations. The method was used to simultaneous determination of barbital, amidopyrine and antipyrine in antondin injection. The experimental data were measured and treated by UV-190 spectrophotometer and microcomputer IBM-PC. The average recoveries of barbital, amidopyrine and antipyrine were 99.1 +/- 1.1% (CV), 99.6 +/- 1.3% (CV), and 99.7 +/- 1.0% (CV), respectively.