diff --git a/Absorption-Imaging-Class.md b/Absorption-Imaging-Class.md
index 385c976..c5ee2c2 100644
--- a/Absorption-Imaging-Class.md
+++ b/Absorption-Imaging-Class.md
@@ -48,7 +48,7 @@ Just for get the absorption imaging, it doesn't require any information about ca
 * **Intensity** *(float, optional)*: Laser beam intensity at the position of atom cloud!
 
 ## absorption_imaging.set_image_name()
-> dylab.absorption_imaging.set_image_name(image, name):
+> dylab.absorption_imaging.set_image_name(image, name)
 
 It can set the searching name of those three satandard images. The defualt names are "atoms", "background" and "dark".
 
@@ -59,13 +59,26 @@ It can set the searching name of those three satandard images. The defualt names
 ### Return
 * Nothing
 
-## absorption_imaging.get_image_absorption
->  dylab.absorption_imaging.get_image_absorption():
+## absorption_imaging.get_image_absorption()
+>  dylab.absorption_imaging.get_image_absorption()
 
-It will calculate the absorption imaging, integrating in \_\_enter\_\_ function
+It will calculate the absorption imaging and update the value storing in **self.absorption_imaging**, integrating in \_\_enter\_\_ function
 
 ### Parameters:
 * Nothing
 
 ### Return:
 * **self.image_absorption** *(2D numpy array, optional)*: A two deminsional numpy array, which stores the calculation result. It will also update the value storing in **self.image_absorption**, so it not necessary to pick up the returned handle.
+
+## absorption_imaging.get_atom_number()
+>  dylab.absorption_imaging.absorption_imaging.get_atom_number(force_to_run=False)
+
+It will return the value storing in **self.aton_number**. If there is no value, it will calculate the atom number and update the value storing in **self.aton_number**. It is also possible to force the program do the calculation and updating, even there is already an avaliable result.
+
+### Parameters:
+* **force_to_run** *(boolean, optionla)*: if it is true, the program will ingorn the value storing in **self.aton_number**, then redo the calculation.
+
+### Return:
+* **self.atom_number** *(float, optional)*: The number of atoms. It will also update the value storing in **self.aton_number**, so it not necessary to pick up the returned value.
+
+