Background:It is challenging to realize very small beta function and dispersion free colliding region in a limited space.Purpose:Tiny electron beam sizes are required to achieve high flux in ultra-short and intense laser-electron campton scattering facilities.Methods:Beam characteristics for different matching conditions are studied with the presence of various alignment and field errors.Results:Beta function of laser-electron beam spot can be up to 0.01 meter and the dispersion function is zero at the same time.The optimization calculations of some main factors including magnetic field error and mechanical installation error are also performed.Conclusions:A mini-beta scheme with the achromatic treatment can be found to meet the experimental requirements.