Abstract: Remote sensing technology has been used in agricultural statistics since early 1970s in developed countries such as USA and since late 1970s in China. It has greatly improved the efficiency with its accurate, timely and credible information. But agricultural monitoring using remote sensing has not yet been assessed with credible data in China and its accuracy seems not consistent and reliable to many users. The paper reviews different methods and the corresponding assessments of agricultural monitoring using remote sensing in developed countries and China, then assesses the crop area estimating method using Landsat TM remotely sensed data in Northeast China. The ground data were gathered with global positioning system and 40 sampling areas were used to assess the classification accuracy. The error matrix was constructed from which the accuracy was calculated. The producer accuracy, the user accuracy and total accuracy are 89.53%, 95.37% and 87.02%, respectively, and the correlation coefficient between the ground truth data and classification results is 0.96. A new error index σ which measures how much the objective area estimation is apart from the ground truth data, is introduced and the average σ of rice area estimation to the ground truth data is 0.084.