The author detected swine pest maternal antibody came from 0，1，7，14，21，28，35 and 42-day-age piglets born by 6 pigs. The immunity effect after first and second immunity also was observed. The results showed that maternal antibody didn’t existed in 0-day-age piglet without eating colostrums，and the highest level of it occurred in second day，then it gradually degraded. 1~28-day-age piglets were protected by swine pest maternal antibody，some piglets also survived after 35-day-age. The piglets were first immunized in 28~35-day-age. Then the protected rate was 73.3% after 21 days and 93.3% after 28 days. The second immunity occurred in the 31st days after the first immunity. The high level of immune antibody could sustain within 4 month after the second immunity， and the immunity protected rate was 73.3% in the fifth month，and it decreased to 46.7% after 6 months. Therefore， the suggestions were the pigs only needed twice immunity before they were sold and breeding pigs should be immunized after every 6 months again