Because I belive that variance of shock is always positive number and it ranges with 0.001 to 10, then I give a uniform as the prior distribution for variance of shock as following
stderr eps_muzhat,0.001,10, uniform_pdf, ;

But Dynare does not work
Can anyone explain for that whether I use the incorrect syntax?

Or you can skip the prior mean and standard deviation, and write instead:

stderr eps_muzhat, uniform_pdf, , , 0.001, 10;

It is imperative define a uniform prior with the lower and upper bounds .Obviously this only works with the uniform prior. All this is explained in the reference manual.