The invention provides a precise clamping device and an active optical control method of laser frequency multiplication crystals. The device comprises a framework assembly, a crystal press plate, an actuator support, a piezoelectric nano actuator, a spherical press head, a preloaded screw and a piezoelectric ceramic controller. Bottom face positioning of a laser frequency multiplication crystal element is achieved on a boss at the bottom of the front face of the framework assembly. The crystal press plate is installed on the framework assembly to carry out initial preloading on the crystals. The piezoelectric nano actuator is installed on the actuator support, thereby achieving ultraprecise active optical regulation of crystal surface forms. According to the invention, simulation modeling calculation, mechanical assembling preloading and automatic optical adjustment are serially connected in the provided fully closed-loop assembling and correction technology process, so the quality of the crystal surface forms can be effectively improved, and quality of high-power laser light beams is ensured. Finally, quite proper, precise, convenient and highly efficient assembling of optical elements with big diameter-thickness ratio in an inertia constraint fusion device is achieved.