Hello @DahshengSong and welcome to the SAS Support Communities!
Either it's just because you misspelled the procedure name (which is causalmed) or your SAS/STAT version is only 14.2 or older. PROC CAUSALMED was introduced in SAS/STAT 14.3. To find out your version number you can submit:
ANOVA, or Analysis Of Variance, is used to compare the averages or means of two or more populations to better understand how they differ. Watch this tutorial for more.