A novel two-dimensional photonic crystal broadband Y-shaped 1 × 2 beam splitter is proposed. Broadband performance of the 1 × 2 beam splitter can be greatly improved by optimizing the z-axis offset of the dielectric rods adjacent to the input and output waveguides, and the offset along the V-shaped oblique waveguide of the dielectric rods at the junction area. To enhance the optimization efficiency and achieve excellent splitting performance of the 1 × 2 beam splitter, the genetic algorithm is applied to inversely design the above offsets of the 1 × 2 beam splitter. The results show that, in the bandwidth range of 1515 to 1587 nm, the highest and lowest transmittance of the 1 × 2 beam splitter are 99.6% and 97.9%, respectively, the additional loss is <0.1 dB, and the uniformity tends to 0 dB. Finally, the tolerance analysis of the 1 × 2 beam splitter is carried out. When the deviation of each variable reaches ±10 nm, the total transmittance of the 1 × 2 beam splitter in the bandwidth range of 1515 to 1587 nm is still higher than 95.2%, with the additional loss <0.22 dB. Due to the virtues of broad operating bandwidth, high transmittance, good uniformity, and strong robustness, the proposed 1 × 2 beam splitter will have great application prospects in the field of photonic integrated circuits, all-optical communication network, and so on.