The spectra of a flare on YZ CMi, obtained with a temporal resolution of 60 seconds on March 4 1985 and over the range 3600-4400 A, are analysed using a gas-dynamic model. In this model, the optical radiation in the U-band, outside of flare maximum, is produced by a condensation formed during the gas-dynamic process. With the optical continuum described by a Planck function for a temperature of T ≈ 104
K, the emitting source area S ≥ 5 10l7
2. The hydrogen plasma kinetics of an “8 levels plus continuum” model atom are calculated, and it is shown that the low slope of the Balmer decrement, just after the flare maximum, is connected with a large population in the second level of the hydrogen atom.