The invention provides a pretreatment device for multi-element material, wherein the device can be used for treating multi-element material by a variable-pitch double helix structure, so that the grains of the material are kept less than 20mm, the material mixing effect is good, the source of raw material is expanded, and the hazard-free treatment quantity of organic waste is extremely improved; furthermore, the device has the integrated functions of cutting, smashing and mixing, so that the power is greatly reduced, the speed is controlled to be less than 300rpm, and the device is small in vibration and noise; a nutrition preparation device comprises a material nutrition preparation storeroom, according to the viscosity situation reflected by the type of the raw material and the probe head of a sensor, the added waste water and nutrient can be ensured from the material nutrition preparation storeroom, and the raw material can be adjusted, so that the material is balanced in nutrition, and the gas generation rate and the stability can be improved; and the cost of the pretreatment device is only 1/6 of that of the similar pretreatment device, so that the cost is greatly saved.