The invention relates to a method for preparing hydroxypivalaldehyde through a micro-channel reactor. The problems that in the prior art, reaction time is long, product selectivity is poor, and the raw material conversion rate is low are mainly solved. By means of the method for preparing hydroxypivalaldehyde through the micro-channel reactor, isobutyraldehyde, formaldehyde raw materials and a catalyst are mixed completely through a pre-mixer of the micro-channel reactor and then enter a constant-temperature reactor of the micro-channel reactor to react, and the product containing hydroxypivalaldehyde is obtained; the mass ratio of formaldehyde to isobutyraldehyde in the raw materials is (1-1.4) : 1; the using quantity of the catalyst is 0.5-5% of the total mass of a reaction solution; reaction temperature in the micro-channelconstant-temperature reactor is 100-140 DEG C, the pressure of a reaction meter is 0.5-1.5 MPa, and the reaction staying time of the reaction solution in the micro-channel reactor is 30-300 s; the technical scheme that after reaction, the conversation rate of the raw material isobutyraldehyde in the reaction solution after reaction is larger than 95%, the selectivity of the product hydroxypivalaldehyde is larger than 95% well solves the problems, and the method can be used for preparing hydroxypivalaldehyde.