Abstract: During Mar. 20-Apr. 3 of 1986 a photoelectric photometry for the Halley's comet is taken by using the 60 cm telescope at Yunnan Observatory. The diaphragm used was 2 mm which corresponds to a field of view about 33". Six standard narrow filters were used in the observations.It is obvious from these results that in the comet there was a violent outburst which occurred after Mar. 21 but before Mar. 26. During the period of this outburst the magnetudes in the bands of C₃, CO⁺ + N₂⁺ and two continua were much brighter than before and after, even brightening up to 4.41 magenitudes in the band of CO⁺ + N₂⁺. By contrast, the variations in the C₂ and CN bands were quite small. After Mar. 26 everything recovered to normal.In its analysis and discussion about this outburst phenomenon, the possible mechanism and chemical reaction processes involved is present.