diff --git a/inc/hgl/math/Matrix.h b/inc/hgl/math/Matrix.h
index 5c84df0..4bebb65 100644
--- a/inc/hgl/math/Matrix.h
+++ b/inc/hgl/math/Matrix.h
@@ -110,7 +110,7 @@ namespace hgl
      * @param target 目标位置
      * @param up 向上向量
      */
-    Matrix4f lookat(const Vector3f &eye,const Vector3f &target,const Vector3f &up);
+    Matrix4f lookat(const Vector3f &eye,const Vector3f &target,const Vector3f &up=AxisVector::Z);
 
     inline Matrix4f translate(const Vector3f &v)
     {
diff --git a/src/Math/Matrix4f.cpp b/src/Math/Matrix4f.cpp
index 0fce0a6..92e91bf 100644
--- a/src/Math/Matrix4f.cpp
+++ b/src/Math/Matrix4f.cpp
@@ -81,7 +81,7 @@ namespace hgl
         float f = 1.0f / tanf( deg2rad( 0.5f * field_of_view ) );
 
         return Matrix4f(
-          f / aspect_ratio,
+          -f / aspect_ratio,
           0.0f,
           0.0f,
           0.0f,