The invention discloses a modified plastic shell for a capacitor. The modified plastic shell is composed of polybutylene terephthalate, ABS plastic, a filling agent, color master batch, dimethyl trimethylsilylmethylphosphonate, polyvinyl chloride resin, a lubricating agent and a modifier. The modifier is composed of, by weight, carboxycellulose, sorbitan trioleate, rosin, sodium hexametaphosphate, alkali lignin, acrylamide, kieselguhr, sodium tripolyphosphate, methyl salicylate, camellia oil and peppermint oil. The prepared capacitor plastic shell is good in mechanical performance and processability, low in cost and melt viscosity and good in shock strength and thermal aging resistance and has excellent heat stability. A small amount of the prepared modifier can achieve the increase function obviously.