$ rpm -ivh xchm-1.2-1.src.rpm
xchm-1.2-1.src.rpm: not an rpm package (or package manifest):
??? what happend
How do I install this type of rpm(*.src.rpm)?

src.rpm are source rpms meaning they contain the source file and a spec file which is used to build the rpm to match your system. What it does with that commmand is it extracts the contents to /usr/src/redhat/ Specs and other directories there. Then you can use the rpmbuild command to build the rpm from the spec file.
rpmbuild -ba file.spec

Or to shorten the process use the rpmbuild command directly to the src.rpm file like so.
rpmbuild --recompile -- rebuild file.src.rpm

When it finishes completely with no errors then the rpm will be in /usr/src/redhat/RPMS

Brian1

It looks like the file you downloaded is corrupted or maybe you downloaded the link to the file instead. Use "file xchm-1.2-1.src.rpm" to see what type of file it is.