diff --git a/brainpy/_src/math/surrogate/_one_input_new.py b/brainpy/_src/math/surrogate/_one_input_new.py
index 64c7280d0..bfffd88f5 100644
--- a/brainpy/_src/math/surrogate/_one_input_new.py
+++ b/brainpy/_src/math/surrogate/_one_input_new.py
@@ -90,7 +90,30 @@ def _as_jax(x):
 
 
 class Surrogate(object):
-  """The base surrograte gradient function."""
+  """The base surrograte gradient function.
+
+  To customize a surrogate gradient function, you can inherit this class and
+  implement the `surrogate_fun` and `surrogate_grad` methods.
+
+  Examples
+  --------
+
+  >>> import brainpy as bp
+  >>> import brainpy.math as bm
+  >>> import jax.numpy as jnp
+
+  >>> class MySurrogate(bm.Surrogate):
+  ...   def __init__(self, alpha=1.):
+  ...     super().__init__()
+  ...     self.alpha = alpha
+  ...
+  ...   def surrogate_fun(self, x):
+  ...     return jnp.sin(x) * self.alpha
+  ...
+  ...   def surrogate_grad(self, x):
+  ...     return jnp.cos(x) * self.alpha
+
+  """
 
   def __call__(self, x):
     x = _as_jax(x)
@@ -123,7 +146,7 @@ def __init__(self, alpha: float = 4.):
     self.alpha = alpha
 
   def surrogate_fun(self, x):
-    return sci.special.expit(x)
+    return sci.special.expit(self.alpha * x)
 
   def surrogate_grad(self, x):
     sgax = sci.special.expit(x * self.alpha)
diff --git a/brainpy/math/surrogate.py b/brainpy/math/surrogate.py
index 0121bddec..bf7897435 100644
--- a/brainpy/math/surrogate.py
+++ b/brainpy/math/surrogate.py
@@ -1,8 +1,9 @@
 # -*- coding: utf-8 -*-
 
 
-
 from brainpy._src.math.surrogate._one_input_new import (
+  Surrogate,
+
   Sigmoid,
   sigmoid as sigmoid,