A photolithography method and system based on a high step slope are provided. The method includes: S1, manufacturing a sacrificial layer with a high step slope on a substrate; S2, adopting a spin-on PR coating process to cover the sacrificial layer with a photoresist layer to form a photolithographic layer; S3, forming a mask pattern and a compensation pattern on a mask; and S4, performing photolithography processes, by a photolithography machine, on the photolithographic layer. By forming a slope-top compensation pattern and a slope compensation pattern on a mask to perform photolithography on the substrate of a sacrificial layer, a relatively wide compensation pattern is set in a part of the top of the slope with a small thickness, thereby compensating the overexposure at the top of the slope, reducing the error in the photolithographic pattern, and improving the precision of photolithography of the high step slope.