1. A calibration method for the brittle fracture assessment parameters for materials based on the Beremin model, the method comprises the following steps: (1) Selecting at least two types of specimens made of a same material but with different constraints, and calculating the fracture toughness value K 0 corresponding to 63.2% failure probability for each type of specimens at a same calibration temperature by using the respective fracture toughness data; (2) Constructing finite element models for each type of specimens using the stress-strain curve of the material measured at the same calibration temperature, and calculating the maximum principal stress σ 1,i and element volume Vi of each element at K=K 0 in each model, where K is a stress intensity factor that describes the intensity of far field loading on the crack front, and i is an order number of elements; (3) Assuming a series of values of the Weibull slope m and calculating a set of values of the Weibull scale parameter σ u for each type of specimens according to the following equation, and plotting the Beremin's parameters characteristic curves for each type of specimens with the curves representing the relationship between m and σ u for each type of specimens; σ u = ∑ i n ⁢ ( σ 1 , i ) m ⁢ V i V 0 m wherein, n represents the number of elements in the fracture process region, V 0 represents a reference volume; (4) Determining the brittle fracture assessment parameters for the material according to the coordinates of the intersection of the Beremin's parameters characteristic curves; (5) using the brittle fracture assessment parameters in safety engineering.