The mackerel and scad fishing grounds in northern part of Taiwan was located at the socalled “Kuroshio current front” in spring season, and the school of fish accumulatenear by the Kuroshio current front ( i. e., the water of continental shelf and theKuroshio current was separated apart by it). The intrusion of the Kuroshio current werehappened all the year round in study area. In summer time, the peak season of the coldring was formed in northern part of Taiwan. The high value of nutrient and thechlorophyll a is located at the center of the cold ring, in this case, we should find a lot offish school accumulate at the center of cold ring, but on the contrary, there are no fishin it but just near by of the cold ring. In winter season, the mass water of sub-layerKuroshio current with high temperature and salinity, become the main sources ofTaiwan warm current, intrude into down layer of the continental shelf water in EastChina Sea, and we found that the mackerel and scad accumulate in this area for wintertime. It is not easy to allure the fish to swim upward by using fishing lamp.The Japanese type purse seine and Danish seine were the two main fishing gearsoperated in northern waters of Taiwan. Comparing with the Danish seine, thepersonnel expenditure was occupied the most of the commercial fishing cost of the purseseine, it is not a good fishing gear and method to catch low value of mackerel and scadthis year.To calculate and analyze both CPUE value and the cost of operation for purse seineand Danish seine, and their results will as a reference given to the government for the fishery policy, and further study of fishing density of the mackerel and scad is needed inthe near future.