@Joe Riel 
Thank you so much!
now i understood the selectremove clearly and can solve my problem with your help!

Best regards,

I'm sorry, i tried to use "" Maple Math" in this forum but i don't know why it cannot display so i tried to figure out my problem by the image that with very similar equations, if i didn't add more "b" it will not return to zero.
these is the text code and Maple worksheet file!
Thank you!

eq1 := 2*e^(a*x)*sin(x)*ln(y);

result,eq1 := selectremove(has,eq1,z);

eq2 := b+2*e^(a*x)*sin(x)*ln(y);

result,eq2 := selectremove(has,eq2,z);

 problem.mw