On Sun, 2 Mar 2014, 罗晨星 wrote:

> Inspired by
> http://tex.stackexchange.com/questions/150566/minionpro-including-math-in-context,
> I also tried the \definefallbackfamily, it turn out to be an undefined
> control sequence.

You need a newer version of ConTeXt (2013.12.20 or newer). Use context 
--version to find the version that you are using. The easiest way to 
update is to install context minimals.

Aditya