The increasing of pulp yield in cooking process is very important for pulppaper industry. The modified kraft cooking, such as polisulfide process, is one of the directions in increasing of pulp yield.We have developed and patented in Russia the method and the devise for its realition. This method is founded on influence of electric spark discharge, in form of highfrequency pulses, on white liquor or lixivium, which contains a wood-pulp material. Current pulse was .generated by low inductance capacitor bank. Current amplitude has the order 30k.4, periode -2Omks. The spark was initiated in liquor. The influence of single pulse or pulse series has been studiedWe have noticed variation of composition of liquor cooking in high-frequency pulse treatment. We have noticed in process of treatment an increasing of NaOH, decreasing of H2S, variations in containing Na2S203 and Na2SOI with polisulfide generation.Cooking of several types of wood cheeps with solutions which had been treated of high-frequency current pulses, shows an increase of pulp yield in a range of 0,9 -2,7% (as to control).