The invention discloses a polymerizable benzophenone photoinitiator (shown in the following formula) containing amine used as an auxiliary initiator and a preparation method thereof, which comprises the following steps: carrying out Friedel-Crafts acylation reaction on tertiary amine containing a benzene ring and 4-nitro benzoyl chloride used as raw materials under the catalytic action of anhydrous aluminum chloride used as a catalyst to generate substituted benzophenone containing a nitro group and a tertiary amino group; then reducing the nitro group into a primary amino group in the presence of stannous chloride and concentrated hydrochloric acid; and reacting acryloyl chloride or methacryloyl chloride with the primary amino group to introduce a polymerizable double bond group to the molecular structure, thus acquiring the polymerizable benzophenone photoinitiator containing amine used as the auxiliary initiator. Because the photoinitiator structurally contains the polymerizable group, the problems of toxicity and high mobility existing in the conventional small molecule photoinitiators can be avoided during photocuring; and in addition, the photoinitiator structurally contains the auxiliary initiator group (tertiary amino group), so that the additional auxiliary initiator does not need to be added during photocuring, and the initiation efficiency is high. Thus, the photoinitiator has a wide application prospect in the photocuring field.