The miraculin-like protein gene MLP2-2 is a H2B protein interaction gene in kumquat. Bioinformatics analysis of the MLP2-2 gene found that the coded protein has a transmembrane domain and has homology with the Kunitz protease inhibitor. Two-year-old kumquat seedlings were subjected to cold acclimation, and the leaf RNA was extracted to obtain the cds sequence by reverse transcription to construct the pBRT7-MLP2-2 over-expression vector, then it was transferred to Rosetta (DE3) Escherichia coli engineered bacteria to express the target MLP2-2 protein. The effect of MLP2-2 on protein degradation rate of total protein extraction from kumquat leaves was detected. The results show that MLP2-2 inhibited kumquat protein degradation by 16%, indicating MLP2-2 have protease inhibitor activity.