With different biochar amount levels of 0t/hm2, 25t/hm2, 50t/hm2, 75t/hm2 and 100t/hm2, the runoff plots experiments were conducted to study the influences of biochar supply on the indexes of soil physicochemical properties, water holding capacity, soil and water conservation and the effects of water-saving and yield-increasing, and a model was established based on Gumbel Copula function for black soil productivity evaluation under different straw biochar amounts. The results showed that with the increase of straw biochar amount, the soil bulk density was decreased and porosity were increased, the soil nutrients distribution was uniform. Available P and K, pH value and organic matter content were increased linearly, and ammonium N was increased exponentially. Saturated soil moisture, field capacity, wilting coefficient and the maximum effective water content were all in positive correlation with the straw biochar amount, and the influence degree of high biochar amount on soil moisture was more significant than that of low biochar amount. With the increase of straw biochar amount, the amounts of annual runoff and soil erosion were all decreased linearly, the reduction rates of runoff and sediments were increased logarithmically, while the soybean yield and water use efficiency were increased firstly and then decreased like a parabola going downwards. The evaluation model based on Gumbel Copula function was used to evaluate the soil productivity under different straw biochar amounts, and the result was reasonable. The soil productivity index calculated by the model was increased with the increase of straw biochar amount in an S-shaped curve, the indexes of soil physicochemical properties, water holding capacity, effect of soil and water conservation were increased linearly, and the indexes of water-saving and yield-increasing were increased firstly and then decreased in a parabola shape. 