Effects of the various colchicine treatments on 2n pollen induction in Dendrobium officinale were carried out in the current work. Cytological mechanism of 2n pollen formation were also studied. The results showed that the optimum method for 2n pollen induction was injecting 0.1% colchicines into the flower buds at about 5.53 mm long and 2.3 mm wide for 3 times, once a day，with the highest induction rate up to 6.22%. the diameter of 2n pollen was 49% larger than n pollen. The abnormal phenomena like parallel spindles and tripolar spindles at meiotic metaphase Ⅱ,triads and dyads at the tetrad period were observed, so the abnormalities in spindle positioning may be one of the cytological mechanism of 2n pollen formation in Den. officinale, and its 2n pollens were genetically equivalent to FDR (first division restitution)type.