In this study,ferrous oxalate was prepared from ferrous sulfate and oxalic acid by precipitation reaction.The effect of the reaction conditions,such as reaction temperature,reaction time,reaction mode,laying-aside time,ball mill time and additive agents on the average particle size of ferrous oxalate was investigated.The optimal reaction conditions for the particle size of ferrous oxalate were obtained as follow: reaction temperature of 20℃,reaction time of 55min,reaction mode of ultrasound,laying-aside time of 30min after titrating,ball mill time of 120min and adding ethanol absolute with the proportion of 3/4 in the dissolution of oxalic acid.Under these optimal conditions,the average particle size which represented by D50 of prepared sample could reach up to 3μm.