The invention discloses an astigmatic compensation type interference detecting device and method for optic free curved surfaces. The device comprises He-He lasers, a
beam expander, a 1 / 2 wave plate, a polarized
beam splitter, a first 1 / 4 wave plate, a second 1 / 4 wave plate, a
standard plane reflector, a phase shifter, a first convergent lens, a to-be-tested free curved surface, a second convergent lens, a plane reflector, a
polarizer, a rotating
frosted glass screen, an imaging objective lens, a
detector, a displayer and a computer. The method comprises the steps of placing the to-be-tested free curved surface in an inclined state to make test beams come in a specific angle in an inclined mode to compensate for main
surface shape astigmatic error components of the to-be-tested free curved surface, therefore reducing the degree of
divergence of the subsequent test beams, and making the stripes discernable on the
detector. The
detector collects a series of phase-shifting interferograms which are treated with a wave front
reconstruction algorithm to obtain a
surface shape of the to-be-tested free curved surface. According to the astigmatic compensation type interference detecting device and method for optic free curved surfaces, the astigmatic compensation method is used for testing optic free curved surfaces for which the main
surface shape error components are
astigmatism, the stability is high, and the cost is low.