An optical magnetic field sensor based on electro-optic compensation and beta-barium borate (β-BaB₂O₄,BBO) crystal is proposed and expe rimentally demonstrated.The proposed optical magnetic field sensing unit is mainly composed of single BBO crystal and two polarizers. By means of light intensity modulation,the sensing light intensity variation ca used by the measurand magnetic field and Faraday effect can be timely compensated by the app lied voltage and electro-optic modulation.Under the condition that the sensing light intens ity is compensated and kept to be constant,the measurement of magnetic field can be conducted by m easuring the electrooptic compensation voltage.The 50Hz ac magnetic flux density has been m easured in the range of 167Gs by use of a block of BBO crystal with dimensions of 4mm×4mm× 20mm.The compensation voltage can be decreased by choosing a proper deviation angle betwe en the probing light beam and the principal optical axis of the BBO crystal,e.g.,0.76°.In th is case,a typical electrooptic compensating voltage is about ~0.0183V·Gs －1,which is approximately 30times lower than the experimental result previously reported.Main advantages of the propose d magnetic field sensor include better insulating ability,lower disturbance to the measurand mag netic field,broader dynamic measurement range,and potential closed-loop measurement of magnetic fi eld.