The law of gas-liquid two-phase flow in microchannel is the main factor affecting the heat transfer coefficient and flow field temperature uniformity of microchannel heat exchanger. Using N2 and H2O as working fluids, the initiation, development, and stability of gas-liquid two-phase flow pattern in discontinuous and parallel rectangular microchannel heat exchangers and the uneven flow distribution in parallel channels are numerically simulated. The results show that the inlet Re of the two-phase working medium has an important influence on the evolution process and flow cycle of the flow pattern in the microchannel: when the inlet Re is 450, the gas phase working medium diffuses into the microchannel in a discrete "bulk" shape in the flow sharing cavity, and the gas phase working medium in the parallel channel gradually changes from a slug shape to a bubble shape; When the inlet Re rises to 1600, the gaseous working medium diffuses into the microchannel in a continuous "elliptical" shape in the flow sharing cavity, and the gaseous working medium in the parallel channel gradually changes from annular flow pattern to bubble flow pattern. The channel structure also affects the uniformity of flow distribution between parallel channels. The existence of discontinuous microcavity improves the uniformity of working medium mass flow distribution in the microchannel by 38.7%. By studying the pressure distribution law in the channel, it is found that the uneven distribution of static pressure in the channel is an important reason for the uneven distribution of two-phase working medium when entering the microchannel from the flow sharing cavity. By changing the inlet structure to ensure the uniform distribution of static pressure in each channel, combined with the discontinuous microcavity between continuous channels, the temperature uniformity of flow field can be better guaranteed and better heat transfer performance can be obtained.