Abstract: Three fragmentations with different degrees had occurred successively for Russian Cosmos 2421 satellite in the first half of year 2008 which produced several hundreds debris. This paper analyzed the three fragmentations and fragmentation debris orbit distribution, velocity increment distribution, area-to-mass ratio and their lifetime according to two-line elements data of Cosmos 2421 satellite and its debris, also made risk evaluation of fragmentation debris to spacecrafts. The results indicate that the three fragmentation dates were March 14, April 28 and June 9 respectively. The fragmentation debris were distributed within 200~1400 km altitude range. The three velocity increments mean values of fragmentation debris in space due to Cosmos 2421 satellite breakup were -8.4 m/s, 8.6 m/s, -8.3 m/s respectively. The lifetime of 67 percent fragmentation debris were within one year. Space debris density below 500 kilometers increased because of the breakup event which affected the manned spacecrafts. It can be seen by analyzing the Cosmos 2421 satellite fragmentation events that breakup events characteristic can be concluded by fragmentation debris characteristic, and the effects to the future launch activity and in-orbit satellite due to breakup events can be evaluated by space density and lifetime computation of fragmentation debris.