文[1]给出了椭圆和双曲线切线的一个性质,笔者经过思考还发现抛物线切线的一个性质,算是对文[1]的补充和完善.性质1若P为抛物线y2=2px(p>0)上不同于坐标原点O的任意一点,直线PO交直线l:x=t于点M,直线PN⊥直线l,垂足为N,以点P为切点的切线交直线l于点Q,则Q为MN的中点.证明如图1,设P(x0,y0),则y20=2px0,N(t,y0). In [1], a property of elliptic and hyperbolic tangent is given. After thinking, we also find a property of parabola tangent which can be regarded as complement and refinement of [1] .Property 1 If P is parabola y2 = 2px (p> 0) at any point different from the origin O of the coordinate PO line l: x = t at point M, straight line PN⊥ straight line l, droop is N, , Then Q is the midpoint of MN. Prove as Figure 1, suppose P (x0, y0), then y20 = 2px0, N (t, y0).