According to the statistics of straight thread sucker rods' application in screw pump in Daqing Oilfield before 2000, the proportion of sucker rods' yearly breakaway reached to 41.6%, taking up 70% of the total wells that were checked. Thus it can be seen that the rods breakaway problem was becoming the main barrier restricting screw pump large-scale population and application. Since then, the development work on the special sucker rods for screw pump had been carried on. Through the analysis on the failure position and failure form of the sucker rods', the following conclusions are presented: (1) The straight thread rod connection doesn't suit for screw pump very well; (2) Essential overload protection and movement limitation are not available; (3) The amount of rod centralizers and their installed position lack of technical basis; (4) Sucker rod's materials and processing quality don't meet the demand. `
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