This is one way to do it -- load all sheets into a dictionary of dataframes and then concatenate all the values in the dictionary into one dataframe.
import pandas as pd
Set sheetname to None in order to load all sheets into a dict of dataframes
and ignore index to avoid overlapping values later (see comment by @bunji)
df = pd.read_excel('tmp.xlsx', sheet_name=None, index_col=None)
Then concatenate all dataframes
cdf = pd.concat(df.values())
print(cdf)
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…