A design method (100, 200) of a diffractive optical assembly, comprising: designing a first diffractive optical element (901, 1301) according to a first target light field; characterized in that the design method (100, 200) further comprises: measuring or simulating the first diffractive optical element (901, 1301) to obtain a first light field difference between a light field of the first diffractive optical element (901, 1301) and the first target light field; and calculating a second target light field according to the first light field difference and designing a second diffractive optical element (902, 1302) according to the second target light field; combining the first diffractive optical element (901, 1301) and the second diffractive optical element (902, 1302) to form a first diffractive optical assembly, so that an incident light beam simultaneously covers the first diffractive optical element and the second diffractive optical element so as to compensate the non-uniformity of the light field distribution of the first diffractive optical element, wherein the first light field difference is a uniformity difference; and the second light field difference between the superposition light field of the first diffractive optical element (901, 1301) and the second diffractive optical element (902, 1302) and the target light field is less than the first light field difference. designing a first diffractive optical element (901, 1301) according to a first target light field; characterized in that the design method (100, 200) further comprises: measuring or simulating the first diffractive optical element (901, 1301) to obtain a first light field difference between a light field of the first diffractive optical element (901, 1301) and the first target light field; and calculating a second target light field according to the first light field difference and designing a second diffractive optical element (902, 1302) according to the second target light field; combining the first diffractive optical element (901, 1301) and the second diffractive optical element (902, 1302) to form a first diffractive optical assembly, so that an incident light beam simultaneously covers the first diffractive optical element and the second diffractive optical element so as to compensate the non-uniformity of the light field distribution of the first diffractive optical element, wherein the first light field difference is a uniformity difference; and the second light field difference between the superposition light field of the first diffractive optical element (901, 1301) and the second diffractive optical element (902, 1302) and the target light field is less than the first light field difference. measuring or simulating the first diffractive optical element (901, 1301) to obtain a first light field difference between a light field of the first diffractive optical element (901, 1301) and the first target light field; and calculating a second target light field according to the first light field difference and designing a second diffractive optical element (902, 1302) according to the second target light field; combining the first diffractive optical element (901, 1301) and the second diffractive optical element (902, 1302) to form a first diffractive optical assembly, so that an incident light beam simultaneously covers the first diffractive optical element and the second diffractive optical element so as to compensate the non-uniformity of the light field distribution of the first diffractive optical element, wherein the first light field difference is a uniformity difference; and the second light field difference between the superposition light field of the first diffractive optical element (901, 1301) and the second diffractive optical element (902, 1302) and the target light field is less than the first light field difference.