The invention discloses a method for improving the extracellular expression level of a foreign protein by means of phospholipase fusion expression. Four proteins, PLA2, MBP, CBD and SUMO, are used as a fusion tag to construct a fusion gene. Compared with an original protein MOH without any fusion tag, the extracellular expression level and enzymatic activity of all the four fusion proteins are increased to some degree. Among them, the fusion protein using PLA2 as the fusion tag has the highest expression level, which is 7.4 times higher than that of the original protein. Compared with other fusion tags, PLA2 has a low molecular weight and the fusion protein having PLA2 as the fusion tag has the highest expression level (up to 12 g·L−1 in a 7 L fermentation tank for high-density fermentation). It is shown that the secretory expression of a foreign protein can be effectively increased by using PLA2 as a fusion tag.