diff --git a/README.md b/README.md
index 498609f..56037a4 100755
--- a/README.md
+++ b/README.md
@@ -1,6 +1,27 @@
-### Guan: an open source python package. The official website is https://py.guanjihuan.com.
+## Guan package
 
-### Installation: pip install --upgrade guan
+Guan is an open source python package, dealing with tight-binding models by calculating band structures, density of states, quantum transport, topological invariant, etc. Other trivial functions are also integrated, including file reading/writing, figure plotting, data processing. The official website is https://py.guanjihuan.com.
 
-### Usage: import guan
+## Installation
 
+pip install --upgrade guan
+
+## Usage:
+
+import guan
+
+## Summary of API Reference
+
++ basic functions
++ Fourier transform
++ Hamiltonian of finite size systems
++ Hamiltonian of models in the reciprocal space
++ band structures and wave functions
++ Green functions
++ density of states
++ quantum transport
++ topological invariant
++ read and write
++ plot figures
++ data processing
++ others