diff --git a/main.py b/main.py
index 4b8785c..7b62296 100644
--- a/main.py
+++ b/main.py
@@ -145,18 +145,12 @@ def run_egm(para: Parameter, animation=None) -> dict:
                     rg_y = gc_y[phase_conductor_foo + 2]
                 else:
                     rg_type = "g"
-            # TODO 保护角公式可能有问题，后面改
+            # 使用实际高度（考虑弧垂）计算保护角
             shield_angle_at_avg_height = (
-                math.atan(
-                    (rc_x - rs_x)
-                    / (
-                        (h_arm[0] - string_g_len - h_arm[phase_conductor_foo + 1])
-                        + string_c_len
-                    )
-                )
+                math.atan2(rc_x - rs_x, rs_y - rc_y)
                 * 180
                 / math.pi
-            )  # 挂点处保护角
+            )
             logger.info(f"地线保护角{shield_angle_at_avg_height:.2f}°")
             logger.debug(f"最低相防护标识{rg_type}。（g表示地面，c表示下导线）")
             rated_voltage = para.rated_voltage