The invention discloses a preparation process for vegetable insulation oil having a low pour point. The process comprises the following steps: a) ultrasonic decoloration treatment; b) deep deacidification treatment; c) dehydration treatment; d) crystallization fractionation treatment; and e) additive treatment. The process adopts short-time ultrasonic dispersion treatment and compounded use of adsorbents to further improve the decolorization effect of the vegetable insulation oil, thereby avoiding problems of an increased acid value of the vegetable insulation oil and accelerated oxidation andcolor reversion of the vegetable insulation oil; the method adopts a deep deacidification manner of a combination of ''physical deacidification and alkali refining deacidification'', and can reduce the acid value of the vegetable insulation oil to an extremely low level; and the effective combination of crystallization fractionation and additives can make the pour point of the vegetable insulation oil to -25 DEG C or less, and the application requirements in most regions in China can be met. The whole process is simple, easy to operate, low in production cost and high in refining rate, and the prepared vegetable insulation oil has excellent performance, good stability and obvious technical advantages, and fully meets the technical requirements of industrial production.